'U' (ii) was the Japanese offensive against Imphal and Kohima in the Manipur state of Assam in north-eastern India by Lieutenant General Renya Mutaguchi’s 15th Army (7 March/22 June 1944).
Imphal lies in a large and fertile valley in the centre of the Manipur hills of north-eastern India, and in 1941 was a cluster of villages nestling among plantain and bamboo groves, and was ruled by a local prince. The surrounding plain was partially occupied by the shallow and swampy Lake Logtak. The population was mostly Hindu, but about 10% were Moslems, and there was a significant population of nomadic Kukis and more settled Nagas, of whom a small number were Christians. There had been no significant disturbances in the area since a rebellion in 1891.
Imphal is located in a relatively isolated area, with just four roads to the outside world. The most important of these led to the north through a deep valley in the Naga hills at an elevation of some 5,000 ft (1525 m) to the village of Kohima, and thence to the railhead at Dimapur. A more difficult route, the Tiddim Road, led slightly to the west of south through the Manipur river valley in the Chin hills, at elevations of up to 9,000 ft (2745 m) to Tiddim and thence Burma. This was the route which had been used by the British forces retreating from Burma in 1942, and was again employed by Japanese in 'U' (ii). Smaller roads led to the west in the direction of Silchar in Assam and to the south-east in the direction of Tamu in north-western Burma, and this latter was also used by the Japanese in their 1944 invasion.
By 1944 the British had undertaken considerable work to improve the Tiddim Road in preparation for their planned counter-offensive into Burma. This proved nearly impossible as the terrain in the Manipur plain, and especially in the Manipur river valley, is extremely unstable and roadbeds tended to dissolve into mud with the slightest fall of rain. One particularly problematic stretch, about 7 miles (11.25 km) long, had 40 switchbacks and was known as 'The Chocolate Staircase'. The technical solution finally adopted was to construct traditional Indian brick kilns along the road and build up the roadbed out of millions of fired bricks.
The surrounding plain had a number of airfields by 1944, of which the most important were the all-weather fields located just to the north-west of Imphal and at Palel near the foothills at the south-eastern end of the plain. The Palel airfield proved to be vulnerable to Japanese commando raids and its surface had a tendency to break up under the weight of Curtiss C-46 Commando transport aircraft, forcing the British to conduct most of their operations during the battle of Imphal out of the Imphal airfield.
Planned by Mutaguchi under the nominal but often ignored supervision of General Masamitsu Kawabe’s Burma Area Army, which had been created on 18 March 1943 with its headquarters at Rangoon to control the Japanese armies in Burma, 'U' (ii) envisaged an extremely bold attempt to invade north-eastern India, and was initially conceived as a spoiling attack against the Indian IV Corps at Imphal with the object of disrupting the planned 'Capital' major offensive for the year for an advance by Lieutenant General W. J. Slim’s British 14th Army to the Chindwin river and thence Mandalay in central Burma. On his own initiative and for his own reasons including personal aggrandisement, Mutaguchi then enlarged the plan into the first stage of an invasion of India itself and perhaps even the ending of British rule in India. Mutaguchi’s determination was manifested in his roughshod overriding of the various objections raised by the staffs of several headquarters, and approval for the offensive was given by Imperial General Headquarters on 7 January.
The feasibility of the operation, which was scheduled for completion before the advent of the wet monsoon in April brought a temporary halt to operations in north-western Burma and north-eastern India, seemed to Mutaguchi to have been revealed by the 'Longcloth' first Chindit operation, but Mutaguchi wholly ignored the fact that the British undertaking had been made possible by the availability of air transport to keep the columns supplied. The Japanese lacked any such capability, especially as 'U' (ii) was posited on the use of three divisions, and relied on the capture of the great supply dumps at Dimapur and round Imphal.
'U' (ii) involved the 15th Army in an all-out drive to seize the Manipur plain, and in particular Imphal and Kohima, the only logical jumping-off points for the Allied offensive, and so cut the Allied lines of communication with northern Assam, the supply base for Slim’s 14th Army and for the Chinese and American forces commanded in northern Burma and south-western China by Lieutenant General Joseph W. Stilwell.
Mutaguchi had planned such an operation for some time, and 'U' (ii) was timed to coincide with the full development of 'Ha' (iv) in the Arakan western coastal region, where Lieutenant General Shozo Sakurai’s 28th Army, formed on 6 January 1944, had succeeded in attracting the Indian 5th, 7th, 25th and 26th Divisions, as well as the 81st and 82nd (West Africa) Divisions plus one parachute brigade and one commando brigade. The Japanese plan was initially conceived on the basis of a 15th Army strength of four divisions, but Kawabe never in fact planned that Mutaguchi should have Lieutenant General Kaoru Takeda’s 53rd Division when it arrived from Formosa, and Mutaguchi’s plans were further disrupted when the 15th Division, commanded by Lieutenant General Masafumi Yamauchi until he died of malaria during the Imphal battle and then by Lieutenant General Uichi Shibata, was delayed in Thailand building a road from Chiengmai to Toungoo, and therefore arrived tired and ill-equipped to reinforce the 15th Army only on 11 February after the personal intervention of Field Marshal Count Hisaichi Terauchi, commanding the Southern Expeditionary Army Group.
Apart from the 15th Division (51st, 60th and 67th Regiments and 21st Field Artillery Regiment), the other two formations of the 15th Army, which had its headquarters at Maymyo, were Lieutenant General Kotoku Sato’s 31st Division (58th, 128th and 138th Regiments and one artillery regiment) based to the north-east of Homalin, and Lieutenant General Genzo Yanagida’s 33rd Division (213rd Regiment, 214th Regiment and 215th Regiment and 33rd Mountain Artillery Regiment) based at Fort White; Yanagida was superseded for timidity early in the campaign by Major General Nobuo Tanaka. The 33rd Division was supported by Type 95 light and Type 97 medium tanks of the 14th Tank Regiment. Air support of 'U' (ii) was the responsibility of elements of Lieutenant General Noboru Tazoe’s 5th Air Division.
Mutaguchi planned a triple advance from the line of the Chindwin river. In the south the 33rd Division would advance from Kalewa on 7/8 March and divide into three columns, that on the left directed against Tiddim with the 215th Regiment, that in the centre moving against Tongzang with the 214th Regiment, and that on the right comprising Major General Tsunoru Yamamoto’s 33rd Infantry Group (reinforced 213th Regiment with most of the division’s wheeled vehicles) to take Tamu and link with the 15th Division. With their first objectives taken, the left and centre columns were then to join at Tongzang and move to the north against Imphal, where they would cut the track to the west in the direction of Silchar and join the 33rd Infantry Group.
In the centre of the front the 15th Division would move off from Thaungdut on 15/16 March and divide into two columns, that on the left deploying one battalion of the 60th Regiment to link with the 33rd Division's right-hand column on the Shenam Saddle, and that on the right having the 51st Regiment plus parts of the 60th and 67th Regiments for its advance on Sangshak and thence to the south on Imphal in order to cut it off from the north before destroying the 14th Army’s formations in the Imphal plain.
In the north the 31st Division was to depart on its 100-mile (160-km) approach march from the area just to the north of Homalin on 15/16 March and divide into three columns, that on the left having Major General Shigesaburo Miyazaki’s 31st Infantry Group (58th Regiment and 128th Regiment) for its advance via Ukhrul to invest Kohima from the south, that in the centre having most of the 138th Regiment for its move to Jessami and an investment of Kohima from the east, and that on the right having one battalion of the 138th Regiment to invest Kohima from the north and prevent the arrival of Allied reinforcements from Dimapur.
At the insistence of Subhas Chandra Bose, leader of the Azad Hind movement wishing to end British rule in India by force with Japanese assistance, the Indian National Army made a modest contribution to 'U' (ii), although the Japanese had originally intended to use INA units only for propaganda and reconnaissance purposes. Units of Major General Mohammad Zaman Kiani’s 1st Division, initially in the form of Colonel Shah Nawaz Khan’s 1st Guerrilla Regiment (Subhas Brigade) less one battalion which had been sent to Arakan, covered the left flank of the 33rd Division's advance. Later Colonel Inayat Kiani’s 2nd Guerrilla Regiment (Gandhi Brigade) was attached to the Yamamoto Force of elements of the 15th Division and 33rd Division. The Special Services Group, which was later redesignated as the the Bahadur Group, operated as scouts and pathfinders with the Japanese advance units in the opening stages of the offensive, and was tasked to infiltrate through the British lines and encourage units of the Indian army to defect.
Thus the 33rd and 15th Divisions would tackle Imphal (the 33rd Division having most of the army’s armour and heavy artillery), while the 31st Division was tasked with the elimination of Kohima and its pass on the road from Dimapur in the north so that Allied reinforcements could not intervene in the major battle around Imphal.
Mutaguchi expected that his 15th Army could complete 'U' (ii) in some three weeks, after which the army could be supplied from captured British stocks until a road had been driven through from Kalewa to Imphal via Palel just to the north of the Shenam Saddle. The Japanese thus carried supplies of food, ammunition and fuel sufficient for a campaign of only three weeks.
Kawabe was already starting to have doubts about the military and logistical viability of 'U' (ii), and similar thinking was revealed by Tazoe, commanding the much depleted 5th Air Division. Moreover, all of Mutaguchi’s divisional commanders disagreed with the plan to greater or lesser extents. Sato distrusted Mutaguchi’s motives, Yanagita openly mocked his boorish superior as a 'blockhead', and Yamauchi was already very ill and believed that 'U' (ii) would fail. The three divisional commanders' main concerns were centred on the logistical aspects of 'U' (ii). Mutaguchi had assumed that success would be achieved within three weeks, but supplies after that period could be obtained only if the Japanese captured Allied supply dumps, as the torrential rains of the spring monsoon would inevitably make it impossible for the Japanese to use the supply routes from the Chindwin river. A gamble such as that which Mutaguchi now intended to take had worked in the near past, but could no longer be a factor on which reliance could be placed given the Allies' almost total air superiority in the area and the improvement in morale and training of British and Indian troops. Mutaguchi proposed to use herds of buffalo and cattle, assembled from area throughout northern Burma and now to be across the Chindwin river, as meat rations on the hoof. Most of these animals wasted away and died from lack of forage, however, and their meat rotted many miles from the troops they were intended to feed.
Other weaknesses in Mutaguchi’s plan became evident as the operation continued: the Japanese had assumed, for example, that the British would not be able to use tanks on the steep, jungle-covered hills around Imphal, and to facilitate movement and supply, the Japanese left behind most of their field artillery, which constituted their chief anti-tank capability. As a result, the Japanese troops had little protection against tanks.
Based on his experiences in the 'E' (i) campaign in Malaya and Singapore and in the 'B' (iii) conquest of Burma in early 1942, Mutaguchi had decided that British and Indian troops were inherently inferior, ignoring the fact that the troops he had encountered during these campaigns had in general been inadequately trained and poorly led. What Mutaguchi ignored, or perhaps chose to ignore, therefore, was the fact that the Allies had by now largely overcome the administrative and organisational problems which had crippled their early efforts in Burma, and their troops were far better trained and of higher morale and thus more strongly motivated.
Facing the 15th Army, the 14th Army, under the overall control of Admiral the Lord Louis Mountbatten’s South-East Asia Command and General Sir Henry Giffard’s British 11th Army Group, had two corps in the area. These were Lieutenant General G. A. P. Scoones’s Indian IV Corps in the Manipur plain region with its headquarters in Imphal, and Lieutenant General M. G. N. Stopford’s Indian XXXIII Corps farther back, activated only in March 1944 with its headquarters at Dimapur, to hold the valley of the Brahmaputra river and its communications vital to the continued Allied effort in Burma and China. It was the Indian IV Corps which was tasked with preparing and then launching the 14th Army’s planned 'Capital' advance to and then across the Chindwin river, and had three major sub-formations in the form of Major General D. T. Cowan’s Indian 17th Light Division with its headquarter in Tiddim, Major General D. D. Gracey’s Indian 20th Division with its headquarters in Tamu, and Major General O. L. Roberts’s Indian 23rd Division with its headquarters in Imphal, as well as Brigadier R. L. Scoones’s Indian 254th Tank Brigade equipped with Lee medium tanks.
At the time the Japanese were getting under way, the two-brigade 17th Light Division was in position round Tiddim (as far to the north as Tongzang and as far to the south as Fort White), the three-brigade 20th Division was located in the Kabaw river valley between Sittaung and Tamu, and the three-brigade 23rd Division was in reserve at Imphal (less Brigadier F. A. Esse’s Indian 49th Brigade at Ukhrul and Sangshak) with the 254th Tank Brigade.
The Indian XXXIII Corps' most capable subordinate formation was Major General J. M. L. Grover’s British 2nd Division, which was dispersed into several parts of India in jungle camps, and the 14th Army’s reserves were Major General C. E. N. Lomax’s Indian 26th Division and Major General F. W. Festing’s Indian 36th Division.
The 14th Army appreciated that the tactical situation in central Burma made it possible for the Japanese to attempt a long-range infiltration campaign, but Slim incorrectly estimated that the Japanese could deploy only two regiments in such an effort, and therefore raised no objection when 'Thursday' was committed on 5/6 March to deliver Major General O. C. Wingate’s Indian 3rd Division for the second Chindit expedition. However, contingency plans for a Japanese offensive nonetheless existed, Scoones intending to pull the Indian 17th Light Division and Indian 20th Division back to the Imphal plain, where they could be reinforced by Major General H. R. Briggs’s Indian 5th Division of Lieutenant General A. F. P. Christison’s Indian XV Corps and by Brigadier M. R. J. Hope-Thompson’s Indian 50th Parachute Brigade flown in from the Arakan front. Scoones could use then use this concentrated force with armour and overwhelming air support to crush any Japanese offensive.
As the Imphal plain was being prepared as the base area for 'Capital', there were large numbers of non-combatants in the area, and Slim planned in 'Stamina' to fly out these 40,000 men in the aircraft bringing in the Indian 5th Division and Indian 50th Parachute Brigade.
The stage was thus set for the climactic battles of 'U' (ii), which pitted some 120,000 Allied soldiers (nine British, 16 Gurkha and 24 Indian infantry battalions, plus 120 tanks) against slightly fewer than 90,000 Japanese (26 infantry battalions) supported by about 7,000 Indian collaborators of Bose’s Indian National Army, parts of whose 1st Division were allocated, as noted above, to the 15th Division and 31st Division. But while the Japanese could call on no reinforcements (excluding some 4,000 men included in the Japanese total above), Scoones could call on Stopford’s Indian XXXIII Corps, which was much reinforced during the campaign and eventually comprised Grover’s British 2nd Division, Major General F. W. Messervy’s Indian 7th Division, Brigadier L. E. C. M. Perowne’s Indian 23rd Brigade of Wingate’s Indian 3rd Division, Brigadier N. I. Nonweiler’s 3rd Special Service Brigade and Brigadier P. C. Marindin’s Lushai Brigade, in all some 75,000 men (three Gurkha, 11 Indian and 20 British battalions) plus the armour of the 149th Regiment, Royal Armoured Corps.
The key to the defence of Imphal and Kohima by the IV Corps was timely withdrawal and concentration when the Japanese attacked, especially as the 17th Light Division had to fall back about 100 miles (160 km).
Scoones and Slim were surprised by the initial strength and speed of the Japanese advance, which started to cross the Chindwin river on 8 March, and gave the order to fall back on Imphal only on 13 March. Even so, they managed to pull back the Indian 17th Light Division and Indian 20th Division in moderately good order, though the Indian 17th Light Division suffered comparatively heavy casualties and two brigades of the Indian 23rd Division were sensibly detached to the south to aid the Indian 17th Light Division.
The formation closest to the Japanese was the Indian 20th Division, which was based on Tamu and held the area behind the Chindwin river as far to the west as the Kabaw valley, with the Yu river running through it, together with Moreh just a short distance to the north-west of Tamu, where a large supply dump had been established. On 20 March, there was a clash between six Lee tanks of the 3rd Carabiniers and six Type 95 tanks spearheading Yamamoto’s advance from the south, and the altogether outclassed Japanese tanks were destroyed. Gracey was opposed to any retreat, but on 25 March was ordered to detach some of his division to provide a reserve for the Indian IV Corps. As this left the division too weak to hold Tamu and Moreh, Gracey’s formation withdrew to the Shenam Saddle, a complex of hills through which the Imphal/Tamu road ran, after setting fire to the supply dump at Moreh and killing 200 cattle there. The division withdrew without difficulty, mainly as a result of the fact that two of Yamamoto’s battalions from the 15th Division (2/51st Regiment and 3/60th Regiment) were delayed at Indaw in northern Burma by the Chindits and were unable to intervene.
Farther to the south, the Indian 17th Division was cut off by the 33rd Division. Patrols from the division and from 'V' Force, which was an irregular force of locally raised levies and guerrillas, had warned Cowan of a Japanese force advancing against the rear of the division as early as 8 March, allowing Cowan to regroup the division to protect its rear. On 13 March, the 215th Regiment attacked a supply dump at Milestone 109, some 20 miles (32 km) behind Cowan’s leading outposts, while the 214th Regiment seized Tongzang and a ridge, named the Tuitum Saddle, across the road a few miles behind the Indian 17th Division’s main position.
The Indian division began to withdraw on 14 March. At Tuitum Saddle, the 214th Regiment was unable to dig in properly before it was attacked by Brigadier R. T. Cameron’s Indian 48th Brigade on 15 March and suffered heavy casualties before it was driven away from the road. Farther to the north, the Japanese took the depot at Milestone 109 on 18 March, but Indian troops recovered it on 25 March. Cowan had taken steps to secure the most vulnerable point in his division’s rear, which was the bridge over the Manipur river between Tongzang and Milestone 109, and the divisional rearguard crossed this safely on 26 March, demolishing the bridge behind it. The division removed most of the vehicles, food and ammunition from the depot at Milestone 109 before resuming its withdrawal to the north.
Both the Japanese and Indian divisions had suffered heavy casualties. Yanagida, the 33rd Division's commander, was already pessimistic, and was apparently unnerved by a garbled radio message which suggested that one of his regiments had been destroyed at Tongzang. Therefore he did not press the pursuit against the Indian 17th Division, and advanced cautiously despite reprimands from Mutaguchi.
Even so, Scoones had been compelled to send the bulk of his only reserve, Roberts’s Indian 23rd Division, to the aid of the Indian 17th Division. Supplied by parachute drops from Allied aircraft, the two formations made their way back to the Imphal plain, which they reached on 4 April.
Imphal had meanwhile been left vulnerable to the 15th Division. The only force left covering the northern approaches to the base was the Indian 50th Parachute Brigade, which was severely handled in the Battle of Sangshak by the 51st Regiment of the 31st Division on its way to Kohima from the south-east. The 60th Regiment of the same division cut the main road a few miles to the north of Imphal at Kanglatongbi on 28/29 March, while the 51st Regiment advanced on Imphal from the north-east down the valley of the Iril river and the track from Litan, some 23 miles (37 km) to the north-east of Imphal.
However, the earlier 'Ha' (iv) diversionary offensive launched by the 55th Division in Arakan had already failed, and Mountbatten had taken steps to secure the use of transport aircraft normally assigned to the 'Hump' ferry operation over the eastern end of the Himalaya mountains. Slim was able to use these to move Major General H. R. Briggs’s experienced Indian 5th Division, including all its artillery and first-line Jeep and mule transport elements by air from Arakan to the central front around Imphal. The airlift was completed in a mere 11 days. One brigade and a mountain artillery regiment went to Dimapur in the Brahmaputra river valley, but the other two brigades, the field artillery and the divisional headquarters went to Imphal, and the division’s leading troops were in action to the north and east of Imphal by 3 April.
On the Japanese left flank, the Khan’s Subhas Brigade reached the edge of the Chin hills below Tiddim and Fort White at the end of March. From this position, the 2/1st Guerrilla Regiment despatched companies to relieve the Japanese forces at Falam and also to Hakha, from which Khan launched patrols and laid ambushes for the Chin guerrillas under the command of a British officer, in the process taking a number of prisoners. In the middle of May, a force under Khan’s adjutant, Colonel Mahboob Ahmed, attacked and captured the hilltop fortress of Klang Klang. During this time, the 3/1st Guerrilla Regiment moved to the area of Fort White and Tongzang in premature anticipation of the destruction of Messervy’s Indian 7th Division in Arakan, which would have allowed it to canvass for volunteers.
During the early part of the 'U' (ii) offensive, the Bahadur Group seems to have achieved some success in inducing captured Indian soldiers to desert to the INA.
From the beginning of April, the Japanese attacked the Imphal plain from several directions:
Having advanced to the north in parallel columns, the 215th Regiment on the left and the 214th Regiment and 213rd Regiment on the right, almost as far as Bishenpur via Hengtam and Torbung, the 33rd Division attacked toward Imphal from the Bishenpur area, where its arrival had closed a secondary track to the east from Silchar into the Imphal plain. A commando raid succeeded in destroying a suspension bridge, making the Silchar track unusable. The Indian 17th and 23rd Divisions were regrouping after their retreat, and Bishenpur was held only by Brigadier D. A. L. Mackenzie’s Indian 32nd Brigade, detached from the Indian 20th Division. The 215th Regiment advanced through the hills to the west of Bishenpur, almost isolating the British in the village, but suffered severely from British artillery fire. The leading Japanese troops were halted by lack of supplies only 10 miles (16 km) to the south of Imphal. The 214th Regiment and 213rd Regiment, which were advancing directly along the Tiddim Road, were halted in villages 2 miles (3.2 km) to the south of Bishenpur as units of the Indian 17th Division rejoined the battle.
Having already infuriated Mutaguchi by his caution, Yanagida was relieved of command at the end of the month and replaced on 16 May by Tanaka.
Yamamoto’s force attacked the Shenam Saddle, which was held by the main body of Gracey’s Indian 20th Division, on the main road from Tamu into Imphal. This was the only metalled road available to the Japanese, and it was vital for them to break through the Shenam Saddle so that Yamamoto’s tanks and heavy artillery could move forward to attack the main defences around Imphal itself. Only a few miles to the north-west of the saddle, moreover, was Palel airfield, which was one of the only two all-weather airfields in the plain, and therefore vital to the defence.
An initial Japanese attack up the road on 4 April was poorly co-ordinated: the infantry was not ready at the appointed time, and 12 Japanese tanks were caught exposed on the road by British anti-tank guns. Between 8 and 22 April there was heavy fighting for five peaks which commanded the road to the east of the Shenam Saddle. The Japanese captured several of them, but counterattacks regained some of those initially lost, and the casualties on each side were heavy.
After his failure to break though along the road, Yamamoto sent some of his force across rough terrain to the north of the Shenam Saddle on a raid against Palel airfield. The two battalions of Kiani’s 2nd Guerrilla Regiment were involved in this attack. On 28 April, the 2nd Guerilla Regiment attacked Palel, and attempted to persuade some of the Indian defenders to surrender, but the latter rallied after initial hesitation. Another Indian National Army detachment carried out demolitions around Palel, but withdrew after it failed to rendezvous with Japanese units. The Gandhi Brigade was short of rations as it had moved to the attack with supplies for only one day, and also lost 250 men to artillery fire after it withdrew from Palel.
The 15th Division encircled Imphal from the north. Its 60th Regiment seized the British supply dump at Kanglatongbi on the main road linking Imphal and Dimapur a few miles north of Imphal, but the depot had been emptied of food and ammunition.
On 6 April, one battalion of Colonel Kimio Omoto’s 51st Regiment took the important Nunshigum Ridge, which overlooked the main airstrip at Imphal. This was a major threat to the Indian IV Corps, and on 13 April the Indian 5th Division counterattacked, with effective air support, massed artillery fire and the Lee tanks of B Squadron of the 3rd Carabiniers. The Japanese had believed that the slopes of the Nunshigum Ridge were too steep for tanks to climb, and indeed the Lee tank had hitherto not been tried in action on such gradients. The Japanese regiment had very few effective anti-tank weapons, and its men were driven from the ridge with heavy casualties. The attackers also lost heavily: every officer of the Carabiniers and 1/17th Dogra Regiment was killed or wounded.
The Japanese attacks had ended by 1 May, and Slim and Scoones now launched a counterattack against the 15th Division, which was the weakest of the Japanese formations and whose defeat would break the siege of Imphal once Kohima had been recaptured and thereby reopened the road to allow reinforcements to arrive from Dimapur. The progress of the counterattack was slow, the two main reasons being that the start of the wet monsoon had made all movement very difficult, and that the Indian IV Corps' formations were suffering the effects of a number of shortages: although rations and reinforcements could be delivered to Imphal by air, significant quantities of artillery ammunition could not, and current stocks had therefore to be conserved and used sparingly.
The Indian 5th Division, supplemented by Brigadier W. A. Crowther’s Indian 89th Brigade flown in to replace the brigade sent to Kohima, and the Indian 23rd Division (later replaced by the Indian 20th Division) tried to retake the steep ridges, such as the Mapao Spur, held by the Japanese, but found these to be almost impregnable. Allied artillery was usually unable to hit Japanese positions on the reverse slopes, and the troops often stormed the summits of the ridges, only to be driven off by mortar fire and grenades from the positions sited on the reverse slopes. The Indian IV Corps then regrouped. The Indian 23rd Division assumed responsibility for the defence of the Shenam Saddle, while from the end of the May, the Indian 5th Division concentrated on a push to the north from Sengmai up the main road through Kanglatongbi, while the Indian 20th Division advanced along the tracks and the Iril river toward Litan and Ukhrul, thus threatening the 15th Division's lines of supply.
By this time, the Japanese were at the end of their endurance as for some time already they gad been without adequate food, medicine, ammunition and a host of other essentials. Neither the 31st Division fighting away to the north at Kohima nor the 15th Division had received adequate supplies since the start of offensive, and their troops were starving. Sato, commander of the 31st Division on his own initiative ordered his formation to start retreating at the end of May so that his division could find food. This allowed the Indian XXXIII Corps to drive the Japanese from Kohima and start an advance to the south toward Imphal.
The men of the 15th Division were forced to abandon their defensive positions to scavenge for supplies in local villages or on the Japanese lines of communication, and Mutaguchi’s dismissal of the mortally ill Yamauchi, with Lieutenant General Ryuichi Shibata succeeding him on 10 June, changed nothing. After driving rearguards of the 'Miyazaki' Force, which was an independent detachment of the 31st Division, and the 60th Regiment from their delaying positions on the road linking Dimapur and Imphal, the leading troops of the Indian IV Corps and Indian XXXIII Corps met at Milestone 109, some 10 miles (16 km) to the north of Imphal, on 22 June, and the siege of Imphal had been lifted.
Tp the south of Imphal, the Indian 17th Division had moved back into the line against the 33rd Division. During the first half of May, there were several Japanese air attacks on Bishenpur, and heavy fighting for the village of Potsangbam, some 2 miles (3.2 km) to the south, in which the British lost 12 tanks. The surviving crews of the 3rd Carabiniers were later extracted from Imphal by air for the unit to be rebuilt in India.
Cowan planned to break the deadlock on this front by sending the Indian 48th Brigade , commanded from 31 May by Brigadier R. C. O. Hedley, on a wide left-hook movement into the Japanese division’s rear while Brigadier G. W. S. Burton’s Indian 63rd attacked it frontally. At the same time the Japanese division’s temporary commander, Major General Tetsujiro Tanaka, its chief-of-staff, planned to infiltrate through the Indian 17th Division’s front to seize vital objectives in the middle of the Indian positions. Both moves were launched almost simultaneously.
The 2/5th Gurkha Rifles of the Indian 48th Brigade cut the road behind the Japanese on 18 May, but the Indian 63rd Brigade was not able to break through to the battalion and Indian 48th Brigade was forced to fight its way back through the Japanese positions to rejoin the division, in the process suffering heavy losses. Meanwhile, the 214th Regiment had taken hills close to 17th Division’s headquarters on 20 May. Because of the Indian incursion into their own rear, the Japanese were unable to reinforce their forward troops, and over the following week the isolated Japanese were driven from their positions in the middle of the Indian division, many parties being wholly destroyed.
A new and distinctly forceful commander, Tanaka, took command of the 33rd Division on 22 May and ordered repeated attacks, but these served only to reduce many of his division’s battalions to little more than cadres. In June, Tanaka received reinforcements, in the form of one regiment from the 53rd Division and a detachment from the 14th Tank Regiment, which he employed for another attack. After a measure of initial success, the new regiment suffered very heavy losses to artillery fire. By the end of June, the 33rd Division was so depleted that it could make no further effort.
Yamamoto’s force had also suffered heavy casualties, but before withdrawing, made two successful raids on Palel airfield during the first week of July, destroying several parked aircraft.
Toward the end of May, the Indian National Army's 1st Guerrilla Regiment and 2nd Guerrilla Regiment, the latter now commanded by Colonel Malik Munawar Khan Awan, had been redirected toward the Kohima sector of the front. The two units moved to the north across the Japanese rear, but by the time they reached Ukhrul the Japanese had already begun to withdraw, and the two units decided instead to attack Imphal. Here both units suffered some desertions, but not on the scale which the British had expected.
As early as May, many senior Japanese commanders had come to realisation that the 'U' (ii) operation should be terminated. Lieutenant General Hikosaburo Hata, until recently the vice-chief of the general staff, had made a tour of inspection of the headquarters of Terauchi’s Southern Expeditionary Army Group's headquarters in Saigon during a period late in April. On his return to Tokyo, Hata reported pessimistically on the outcome of the operation to the prime minister, General Hideki Tojo, at a large staff meeting, but Tojo dismissed his concerns as their source was a junior staff officer at the headquarters of the Burma Area Army. Messages were then sent from Imperial General Headquarters demanding that 'U' (ii) be fought to the end.
Kawabe had travelled north from his headquarters at Rangoon to assess the situation for himself on 25 May. He spoke with several officers who expressed confidence in success if reinforcements could be provided, but actually concealed their losses and the increasingly serious nature of the situation. At a meeting between Mutaguchi and Kawabe on 6 June, both used an unspoken Japanese form of communication, making use of gesture, expression and tone of voice, to convey their conviction that success was impossible, but neither commander wished to bear the responsibility for ordering a retreat. Kawabe subsequently became ill with dysentery, but nevertheless ordered repeated attacks, stating later that Bose was the key to Japan’s and India’s future.
Mutaguchi ordered the 31st Division, which was now retreating from Kohima as its men were starving, to join the 15th Division for a renewed assault on Imphal from the north. Neither of the divisions complied as both were in no condition to fight any longer. When he realised that none of his formations were obeying his orders to attack, Mutaguchi finally ordered the offensive to be broken off on 3 July. Reduced in many cases to a starving and almost naked rabble, the Japanese fell back to the Chindwin river as best they could, abandoning their artillery, transport, and many soldiers too badly wounded or sick to walk.
The defeat at Kohima and Imphal was the largest purely military reverse ever suffered by the Japanese. They had suffered just less than 55,000 casualties, including 13,500 dead, and it is believed that the majority of these losses resulted from starvation, disease and exhaustion rather than British and Indian action. On the other side of this coin, the British and Indians suffered some 17,500 casualties, slightly more than 12,600 of them in battle. The Japanese had also lost almost every one of the 12,000 pack horses and mules in their transport units, as well as the 30,000 cattle used either as beasts of burden or as rations. This loss of pack animals was to cripple several Japanese divisions in the course of the following year’s fighting.
Allied air power played a vital part in the Battle of Imphal. By the middle of 1944, the Allied air forces enjoyed essentially undisputed air supremacy over Burma. The last major effort by the Japanese army air force had been over Arakan in February and March, when they had suffered severe losses. During the Imphal and Kohima battles, it was able to make barely half a dozen significant raids.
The Indian IV Corps enjoyed close air support by the fighter-bombers and dive-bombers of the RAF’s No. 221 Group. Allied fighter-bombers and medium bombers strafed and bombed Japanese concentrations, supply dumps, transport, roads and bridges all the way to the Chindwin river. The monsoon in no way diminished their activity. The RAF’s 3rd Tactical Air Force increased its sorties to 24,000 during the worst four months of the monsoon, nearly six times the figure of the previous year’s record.
However, the single most important contribution to the Allied victory was made by both British and US transport aircraft. The Allies could fly men, equipment and supplies into the airstrips at Imphal and, until the onset of the monsoon rains, also into Palel, so although cut off by land, the town was not without a lifeline. By the end of the battle the Allied air forces had flown 19,000 tons of supplies and 12,000 men into Imphal, and flown out 13,000 casualties and 43,000 non-combatants. Among the supplies carried during the siege were more than 1 million gallons of fuel, more than 1,000 bags of mail and 40 million cigarettes, and the latter two were of paramount importance in the maintenance of morale. Several thousand mules, many shipped from the state of Missouri in the USA, were used to supply outlying outposts, so animal fodder was also flown into Imphal during the siege. Allied aircraft could also parachute ammunition, rations and even drinking water to surrounded units.
At the start of the battle, the South-East Asia command had available to it 76 transport aircraft, most of them Douglas C-47 Skytrain machines, but many others were dedicated to supplying the nationalist Chinese force under Generalissimo Chiang Kai-shek and to the creation of USAAF bomber bases in China across the 'Hump'. Not even Mountbatten possessed the the authority to commandeer any of these aircraft, but at the crisis of the battle in the middle of March he nevertheless did so, acquiring 20 Curtiss C-46 Commando aircraft, the equivalent of another 30 C-47 machines. In this Mountbatten had the support of US officers at his headquarters and at the US headquarters of the China-Burma-India Theater command.
Even as the Battle of Imphal raged, an altogether smaller but no less important and significantly more bitter struggle was taking place in the Battle of Kohima, which marked the turning point of the 'U' (ii) offensive.
Kohima was a small village in Nagaland, some 60 miles (100 km) to the north of Imphal, as the crow flies, on the main road between the British and Indian base area at Imphal and the nearest railhead at Dimapur, at the 4,738-ft (1444-m) summit of a pass and overlooked by a chain of hills, the Kohima ridge, which is the key feature of the terrain. To its west is a 10,000-ft (3050-m) massif, while the mountains to the north and east reach some 8,000 ft (2440 m). The area is heavily forested except for terraced and cultivated clearings in the immediate area of the village.
The Battle of Kohima was fought in three major stages from 4 April to 22 June. In the first stage, between 3 and 16 April, the Japanese attempted to capture Kohima ridge, a feature which dominated the road by which the besieged British and Indian troops of the Indian IV Corps at Imphal were supplied; and by the middle of April, the small British force at Kohima had been relieved. In the second stage, between 18 April and 13 May, British and Indian reinforcements counterattacked and drove the Japanese from the positions they had captured, at which point the Japanese abandoned the ridge but continued to block the road from Kohima to Imphal. In the third stage, between 16 May and 22 June, the British and Indian troops pursued the retreating Japanese and reopened the road. The battle ended on 22 June when British and Indian troops from Kohima and Imphal met at Milestone 109, ending the siege of Imphal.
The tight physical constraints and the savagery of the fighting have led to the frequent description of the Battle of Kohima as the 'Stalingrad of the East'.
Part of the 'U' (ii) plan involved sending Sato’s 31st Division (58th Regiment, 124th Regiment, 138th Regiment and 31st Mountain Artillery Regiment) to capture Kohima and thus cut off Imphal from the north. Mutaguchi wished to exploit the capture of Kohima, which he believed could be accomplished both easily and swiftly, by pushing the 31st Division on to Dimapur, the vital railhead and logistical base in the Brahmaputra river valley.
Sato was decidedly unhappy with his role, for he had not been involved in any of the planning, had severe doubts about the plan’s viability, and had already told his staff that the division’s men might well all starve to death. Like many other senior Japanese officers, Sato considered Mutaguchi a 'blockhead', and the two men had also been on opposite sides in a factional split within the Japanese army in the course of the early 1930s. Moreover, Sato believed he had reason to distrust Mutaguchi’s motives.
Starting on the night of 15/16 March, the 31st Division crossed the Chindwin river at three points in the area of Homalin and began to move to the north-west along jungle trails on a front almost 60 miles (100 km) wide. The division moved in three main main groupings. On the left, two battalions of Colonel Utata Fukunaga’s 58th Regiment, with most of the division’s supporting elements and followed by the 124th Regiment, was the Left Assault Force (otherwise the 'Miyazaki' Force under Major General Shigesaburo Miyazaki, commander of the 31st Division's infantry group), and this crossed the Chindwin River to the north of Thaungdut and headed for Mollen just over the border into India, and thence Ukhrul and finally Maram to the south of Kohima on the road to Imphal. In the centre, the Centre Assault Force (the rest of the 58th Regiment) crossed the Chindwin river between Homalin and Tamanthi and headed for Fort Keary, Somra, Jessami and Phakekedzum. In the north, the Right Assault Force (138th Regiment) crossed the Chindwin river at Tamanthi and made for Layshi and thence to the north of Jessami as far as Zubza just to the north of Kohima on the road to Dimapur. All being well, this triple advance would put the 31st Division in position for simultaneous assaults on Kohima from the south, east and north.
Although the Japanese advance was hard work, as the division’s three columns were moving along tracks through difficult country rather than on roads, good progress was at first made. The Left Assault Force was farther forward than the neighbouring formation to the south, the 15th Division, when on 18 March it approached the village of Ukhrul, about 25 miles (40 km) to the north-east of Imphal and 8 miles (13 km) to the north of Sangshak.
Early in 1944, Brigadier F. A. Esse’s Indian 49th Brigade of Robert’s Indian 23rd Division had been stationed at Sangshak to guard the road from Tonhe on the Chindwin river to Imphal. As the 'U' (ii) offensive began, the Japanese had surrounded Cowan’s Indian 17th Light Division at Tiddim, well to the south of Imphal, and Scoones had despatched the main strength of the Indian 23rd Division, including the Indian 49th Brigade, to aid the Indian 17th Division in its break out of encirclement.
At the time, the Indian 50th Parachute Brigade was involved in advanced jungle training in the area of Kohima. The brigade comprised the 152nd (Indian) and 153rd (Gurkha) Parachute battalions, together with a single machine gun company, a mountain artillery battery and other supporting arms. Even before the start of 'U' (ii), the brigade had received warning orders to move to Sangshak but, as a result of a shortage of transport, this movement took the four days from 14 to 18 March. At Sangshak, the brigade took under command the 4/5th Mahratta Light Infantry, which had been part of the Indian 49th Brigade, and two companies of the Royal Nepalese army’s Kalibahadur Regiment.
At first the Indian 50th Parachute Brigade deployed over a wide area, with outposts 8 miles (13 km) to the east of Sangshak and the machine gun company at Ukhrul. On 19 March, the Japanese overran an isolated company of the 152nd Parachute Battalion deployed on a hill known as Point 7378, reducing the company to just 20 men. Urged by his second-in-command that the brigade risked defeat in detail should it remain scattered in isolated posts, Hope-Thompson ordered his forces to concentrate. Most of the force initially concentrated at Sheldon’s Corner, 8 miles (13 km) to the east of Sangshak on 21 March, but during the afternoon of this day Hope-Thomson pulled his units back, first to 'Kidney Camp' 4 miles (6.4 km) to the west, and then to Sangshak itself, where they took up a defensive position on a hill just to the east of the village, which had a US missionary church at its northern end. The position measured only 800 by 400 yards (730 by 370 m), lacked any source of potable water, and had hard rock a mere 3 ft (0.9 m) below the soil’s surface, meaning that only shallow trenches could be dug.
The 2/58th Regiment had meanwhile taken Ukhrul from the brigade’s machine gun company, and Miyazaki knew that there was a 'British' brigade at Sangshak. Although Sangshak was in the sector assigned to the 31st Division's southern neighbour, the 15th Division, Miyazaki knew that this formation was lagging behind his force and thus decided to clear the British-officered force from Sangshak so that it could not interfere with his advance. The Japanese battalion attacked Sangshak from the north on the night of 22 March. Miyazaki had been prepared to await the arrival of his regimental guns and some attached mountain guns for support of the attack, but Captain Nagaya, the battalion’s commander, attacked hastily without artillery support and as a consequence suffered heavy losses as a result of British artillery and mortar fire.
One of the Japanese officers killed in the parachute brigade’s positions was found to be carrying vital maps and documents, which contained all of the 31st Division's plans. Hope-Thompson swiftly sent two copies of the documents through the encircling Japanese to the headquarters of the Indian IV Corps at Imphal, and the information proved invaluable in the British response to the Japanese attack on Kohima.
On the following day, 23 March, Allied aircraft tried to drop supplies to the Indian 50th Parachute Brigade, but the latter’s position was so small that many of the supplies came down in Japanese-held areas. The Gurkhas of the 152nd Parachute Battalion attacked to recover them, supported by fighters which had escorted the transport aircraft, but were beaten back. Even so, the Japanese also suffered heavy casualties.
On 24 March the Japanese were reinforced by the 3/58th Regiment, accompanied by the regimental commander and Miyazaki. The newly arrived battalion immediately attacked, and was driven back.
Major Fukushima’s 3/60th Regiment of the 15th Division also began to attack the parachute brigade’s position from the east on 25 March. Although the battalion commander had demanded that a full reconnaissance of the objective be made so that a tactically sound approach could be planned: this was in marked contrast with the practice of the 58th Regiment, whose commander had emphasised the advantages of speed. Even so, the 3/60th Regiment's infantry became lost and it tried to approach the position at night. During the following day, the battalion’s two attached pieces of 75-mm (2.95-in) mountain artillery destroyed many of the defenders' shallow trenches. On 26 March, the infantry of Fukushima’s 3/60th Regiment again became lost in an attempted night attack and were caught in the open at dawn.
The Japanese planned an all-out assault on 27 March despite the fact that Miyazaki had tried to demand that the 58th Regiment should attack on its own so that only it would have the honour of the victory. By this time, the defenders were exhausted and desperately short of water. There were 300 wounded in the position, and the smell of decomposing bodies, which included those of the mules of the attached mountain artillery and the supply column, was night unbearable. At 18.00, Hope-Thompson received orders to withdraw, and the brigade moved out under cover of darkness, although several men were captured by another battalion of the 60th Regiment, which had cut the track from Sangshak to Litan.
The Indian 50th Parachute Brigade had suffered 652 casualties. The Japanese reported capturing 100 prisoners, most of whom were wounded. The Japanese also seized much of the air-dropped supplies which had missed the defenders at Sangshak, and other equipment including heavy weapons, vehicles and radio equipment. The Japanese casualties were also heavy. The 2/58th Regiment was the hardest-hit unit as it had suffered more than 400 casualties. More important for the Allies, however, was the fact that the prolonged battle had also delayed Miyazaki’s advance on Kohima by a week. His Left Assault Force had been moving along the shortest and easiest route to Kohima, but reached at the vital Kohima ridge only on 3 April, by which time Allied reinforcements had also reached the area.
Meanwhile Slim had come to the belated realisation, in part as a result of the Japanese documents captured at Sangshak, that a complete Japanese division was moving on Kohima. Slim and his staff had originally believed that the forbidding terrain and Japanese logistical considerations would have prevented the Japanese from despatching anything more than one regiment to take Kohima.
Slim knew that there were few combat troops, as opposed to men of line-of-communication units and supporting services, in Kohima and none at all in the the all-important base at Dimapur, which contained an area of supply dumps 11 miles (17.75 km) miles long and 1 mile (1.6 km) wide, some 30 miles (48 km) to the north. As the loss of Dimapur would have been a disaster for the Allies, Slim asked Giffard for more troops to protect Dimapur and to prepare the relief of Imphal.
The Allies were already involved in a rapid reinforcement of the Imphal front. As part of this move, the infantry and artillery of Briggs’s Indian 5th Division were flown from Arakan, where they had just participated in the defeat of the Japanese 'Ha' (iv) subsidiary offensive in the Battle of the 'Admin Box'. While the main body of the division went to Imphal, where some units had already been cut off and almost all of the Indian IV Corps' reserves had already been committed, Brigadier D. F. W. Warren’s Indian 161st Brigade, together with the Indian 24th Mountain Artillery Regiment, was flown to Dimapur.
Early in March, Perowne’s British 23rd Brigade was removed from Wingate’s Indian 3rd Division, the Chindit force, and sent by rail from the area round Lalaghat to Jorhat, some 50 miles (80 km) to the north of Dimapur, from which it could operate to threaten the right flank of any Japanese attack on the base. Giffard and General Claude Auchinleck, the commander-in-chief of the British and Indian forces in India, also prepared to send Grover’s British 2nd Division and the headquarters of Stopford’s Indian XXXIII Corps from reserve in southern and central India by road and rail to Dimapur.
Until the headquarters of the Indian XXXIII Corps could reach Dimapur, local command was to be exercised by Major General R. P. L. Ranking’s No. 202 Line of Communication Area.
Kohima’s strategic importance within 'U' (ii) rested in the fact that it lay on the summit of the pass which offered the Japanese the best route from Burma into India. Moreover, through this pass ran the road which was the main supply route from the base area at Dimapur in the Brahmaputra river valley and Imphal, where three divisions of British and Indian troops faced the main Japanese offensive.
Kohima Ridge itself extends along an essentially north/south axis. The road from Dimapur ascends to its northern end and then passes along its eastern face. In 1944, Kohima was the administrative centre of Nagaland. The Deputy Commissioner’s bungalow stood on the hillside at a bend in the road, with its gardens and tennis court, and a clubhouse, on terraces above it. Although some slopes round the village had been cleared and terraced for cultivation, the steep slopes of the ridge were densely forested. To the north of the ridge was the densely inhabited area of the Naga Village, crowned by Treasury Hill and Church Knoll, and to the south and west of Kohima Ridge were GPT Ridge and the jungle-covered Aradura Spur.
The various British and Indian service troop encampments in the area gave their names to the features which were to be important in the battle: the location of the Field Supply Depot, for example, became known as FSD Hill or merely FSD. The Japanese later assigned their own code-names to the features: for example, Garrison Hill became known as Inu (dog) and Kuki Piquet as Saru (monkey).
Before the arrival of the Indian 161st Brigade, the only combat troops in the Kohima area were the newly raised 1/Assam Regiment and a few platoons of the paramilitary 3 (Naga Hills)/Assam Rifles. The Indian 161st Brigade deployed in Kohima a a time late in March, but Ranking then ordered it back to Dimapur on the grounds that Dimapur possessed greater strategic importance: Kohima was regarded merely as a roadblock, whereas Dimapur was the railhead round which the majority of Allied supplies were held. Slim also feared that the Japanese might leave only a detachment to contain the garrison of Kohima while the main body of the 31st Division moved by tracks to attack Dimapur. Then, to Slim’s considerable relief, Sato concentrated the 31st Division on the capture of Kohima. It is worth noting that at a time early in the siege of Kohima, on 8 April, Mutaguchi directly instructed Sato to send a detachment to advance on Dimapur: with considerable reluctance, Sato complied and detached one battalion of the 138th Regiment, but a few hours later Kawabe, Mutaguchi’s immediate superior, countermanded the order.
As the Right Assault Force and Centre Assault Force of the 31st Division neared Jessami, some 30 miles (48 km) to the east of Kohima, elements of the Assam Regiment fought delaying actions against them from 1 April. Nevertheless, the men in the forward positions were soon overrun and the Assam Regiment was ordered to withdraw. By the night of 3 April, Miyazaki’s troops reached the outskirts of the Naga Village and began probing into Kohima from the south.
The headquarters of the Indian XXXIII Corps assumed responsibility for this part of the front from Ranking on 3 April, and on the following day Stopford ordered the Indian 161st Brigade to move forward to Kohima once again, but only Lieutenant Colonel J. Laverty’s 4/Queen’s Own Royal West Kent Regiment and one company of the 4/7th Rajput Regiment had reached Kohima before the Japanese cut the road to the west of the ridge. Besides these men of the Indian 161st Brigade, the garrison consisted of one raw battalion, the Shere Regiment, of the Royal Nepalese Army, some companies of the Burma Regiment, elements of the Assam Regiment which had withdrawn to Kohima and various detachments of convalescents and line-of-communication troops. The garrison thus totalled about 2,500 men, but of these some 1,000 were non-combatants. The commander was Colonel H. U. Richards, who had served formerly with the Chindits.
The siege of Kohima started on 6 April, and the garrison was taken under a continuous bombardment by artillery and mortars, including number of these weapon which the Japanese had captured, along with their ammunition, at Sangshak and from other depots. The garrison was slowly driven into a small perimeter on Garrison Hill, on which it had artillery support from the main body of the Indian 161st Brigade, itself cut off 2 miles (3.2 km) away at Jotsoma. As at Sangshak, however, the men of the garrison were very short of drinking water. The supply point for potable water was on GPT Ridge, to the south of Garrison Hill, and this had been taken by the Japanese on the first day of the siege. Some of its defenders had not been able to retreat to other positions on the ridge and instead withdrew toward Dimapur. Canvas water tanks on FSD and at the hospital on the 53rd Indian General Hospital Spur had been neither filled nor dug in to protect them from fire. There was a small spring on the northern side of Garrison Hill, but this could be reached only at night. The medical dressing stations were exposed to Japanese fire, and many wounded men were hit again, often more than once, even as awaited treatment.
Some of the heaviest fighting took place at the northern end of Kohima Ridge round the DC’s Bungalow and tennis court, in what became known as the Battle of the Tennis Court. The tennis court almost immediately became a no man’s land, with the Japanese and the defenders of Kohima dug in on opposite sides, so close to each other that grenades were thrown between the trenches.
On the night of 17/18 April, the Japanese finally captured the area of the DC’s Bungalow. Other Japanese troops took Kuki Picquet between Garrison Hill and FSD, thereby cutting the garrison in two. The defenders' situation was acutely bad, but the Japanese did not immediately follow with an attack on Garrison Hill, and with the arrival of day, troops of Indian 161st Brigade arrived to relieve the garrison.
Grover’s British 2nd Division had begun to arrive in Dimapur at a date early in April and by 11 April the 14th Army had an approximate numerical parity with the Japanese in the area. Brigadier V. F. S. Hawkins’s British 5th Brigade of the British 2nd Division broke through Japanese roadblocks to relieve the Indian 161st Brigade in Jotsoma on 15 April, and Brigadier J. D. Shapland’s British 6th Brigade took over the Indian 161st Brigade’s 'Jotsoma Box' defensive position, making it possible for the Indian brigade to launch an attack toward Kohima on 18 April with air, artillery and armour support. After a day’s heavy fighting, the Indian brigade’s vanguard, the 1/1st Punjab Regiment, broke through and started to relieve the Kohima garrison.
By this point, Kohima resembled a Western Front battlefield of World War I in its devastation, which was characterised by shattered trees, ruined buildings and ground cratered by the detonation of thousands of shells and mortar bombs.
Under cover of darkness, about 300 wounded men were brought out under Japanese fire. Although contact had been established between the garrison and its relievers, needed another day for the road between Jotsoma and Kohima to be secured, and in the course of 19 April and early hours of 20 April, Shapland’s British 6th Brigade replaced the original garrison. At 06.00 on 20 April Richards transferred command of the area.
On 17 April, Sato had received an order from Mutaguchi to take Kohima by 29 April and then send three battalions to the Imphal front. Sato responded to the order with a contemptuous silence, but when the order was repeated he replied that this was impossible. On 25 May Sato was informed that all the available transport for the 15th Army was committed to bringing reinforcements to the 33rd Division and that there would be no supplies for his 31st Division.
Miyazaki continued his units' efforts to capture Garrison Hill, and there was heavy fighting for this position for several more nights, each side suffering significant losses. The Japanese positions on Kuki Picquet were only 50 yards (45 m) from Garrison Hill, and the fighting was often of hand-to-hand nature. On the other flank of Garrison Hill, on the night of 26/27 April, a British attack recaptured the clubhouse above the DC’s Bungalow, which overlooked most of the Japanese centre.
At this stage the Japanese reorganised their units for defence rather than offence. The Left Assault Force, under Miyazaki’s command, held Kohima Ridge with four battalions. Sato’s divisional headquarters and Colonel Shiraishi’s Centre Assault Force held the Naga Village with another four battalions. The considerably smaller Right Assault Force held villages to the north and east.
To support their attack against the Japanese position, the British had grouped 38 3.7-in (94-mm) mountain howitzers, 48 25-pdr field gun/howitzers and two 5.5-in (140-mm) medium guns. The Royal Air Force, in the form largely of the Hawker Hurricane fighter-bombers of No. 34 Squadron and Vultee Vengeance dive-bombers of No. 84 Squadron, also played a major part as its warplanes strafed and bombed the Japanese positions. In opposition the Japanese had only 17 75-mm (2.95-in) mountain guns, and these had very little ammunition.
Even so, the British counterattack made only slow progress, for tanks could not easily be used and the Japanese occupied bunkers which were very deep, well-concealed and sited in mutually supporting locations.
While the British 6th Brigade defended Garrison Hill, the other two brigades of the British 2nd Division attempted to outflank the ends of the Japanese position in the Naga Village to the north and on GPT Ridge to the south. By this time the basic difficulty of the terrain had been compounded by the fast that the monsoon had broken and the area’s steep slopes were now covered in mud, making movement and supply very difficult. On 4 May, Hawkins’s British 5th Brigade secured a foothold in the outskirts of Naga Village but was counterattacked and driven back. On the same day, Brigadier W. H. Goshen’s British 4th Brigade had completed a long flank march around Mt Pulebadze to approach Kohima Ridge from the south-west, and now attacked GPT Ridge in driving rain, capturing part of the ridge by surprise but not managing to secure the entire ridge. Two successive commanders of the British 4th Brigade were killed in the subsequent close-quarter fighting on the ridge: Goschen was killed on 7 May, and Brigadier J. A. Theobalds died of wounds on 16 May.
With both outflanking attacks unsuccessful as a result of the terrain and weather, the British 2nd Division concentrated on attacking the Japanese positions along the Kohima Ridge from 4 May. Fire from Japanese positions on the reverse slope of GPT Ridge repeatedly caught British troops attacking Jail Hill in flank, inflicting heavy casualties and preventing them from capturing the hill for a week. However, the various Japanese positions slowly succumbed to British assault: Jail Hill, Kuki Picquet, FSD and DIS were taken by Brigadier F. S. Loftus-Tottenham’s Indian 33rd Brigade on 11 May after a barrage of smoke shells had blinded the Japanese machine gunners and allowed the troops to secure the hill and dig in.
The last Japanese positions on the ridge to be captured were the tennis court and gardens above the DC’s Bungalow. On 13 May, after the failure of several attempts to outflank or storm the position, the British finally bulldozed a track to the summit above the position so that a tank could be dragged up to it. A Lee tank then crashed down onto the tennis court and destroyed the Japanese trenches and bunkers there. The 2/Dorsetshire Regiment followed and captured the hillside where the DC’s Bungalow had formerly stood, thus ending the clearance of clearing Kohima Ridge.
The area had been reduced to a shattered wilderness in which rats and flies feasted on an abundance of half-buried human remains. The conditions under which the Japanese troops had lived and fought were described by many British witnesses as truly unspeakable.
By this time there were enough British troops in the area for Stopford to rotate exhausted brigades out of the line from time to time for a few days' rest in Dimapur. The Japanese, by contrast, had no reinforcements, no air support and no armour.
The situation worsened still further for the Japanese as yet more Allied reinforcements arrived. Messervy’s Indian 7th Division was now arriving piecemeal by road and rail from Arakan. Its Indian 33rd Brigade had already been released from XXXIII Corps reserve to join the fighting on Kohima Ridge on 4 May; and the divisional headquarters and Brigadier M. R. Roberts’s Indian 114th Brigade arrived on 12 May and, with the Indian 161st Brigade under command, the division concentrated on recapturing the Naga Village from the north. Brigadier G. M. Dyer’s independent Indian 268th Brigade was used to relieve the brigades of British 2nd Division so that these latter could recuperate before resuming their drive to the south along the road to Imphal.
Even so, when the Allies launched another attack on 16 May, the Japanese continued to defend the Naga Village and the Aradura Spur with enormous tenacity. An attack on Naga Hill during the night of 24/25 May made no ground at all, and another attack, directed against both ends of Aradura Spur on the night of 28/29 May, was even more decisively driven back.
These and other setbacks combined with exhaustion and the effects of the climate to play a major part in decreasing morale in the Allied formations and units in general, and in the British 2nd Division in particular.
The decisive factor in the Battle of Kohima was the Japanese units' lack of supplies. The 31st Division had begun 'U' (ii) with food for only three weeks, and once this stock of food had been eaten, the Japanese had to exist on meagre captured stocks and what they could forage in local villages, whose inhabitants became increasingly hostile. It is worth noting that just before the start of their siege of Kohima, the Japanese had captured a large warehouse in the Naga Village with sufficient rice to feed the division 'for three years', but this had immediately been bombed and the stock of rice destroyed. To add to the Japanese supply difficulties, the British 23rd Brigade, which had been operating behind the 31st Division, had cut the Japanese supply lines and prevented the Japanese from foraging in the Naga hills to the east of Kohima. The Japanese had undertaken a pair of resupply missions, using captured Jeeps to carry supplies from the Chindwin river to the 31st Division, but the undertakings delivered mainly artillery and anti-tank ammunition rather than food.
By the middle of May, as the men of the 31st Division starved, Sato decided that Mutaguchi and the headquarters of the 15th Army were taking little notice of his situation, as they had issued several confusing and contradictory orders to him during April. Because the main attack on Imphal had faltered in about the middle of April, Mutaguchi wished the 31st Division, or at last major parts of it, to join the assault on Imphal from the north even as the division was struggling to take and hold Kohima. Sato considered that the 15th Army's headquarters was issuing wholly unrealistic orders to his division with no proper planning or even with any real consideration of the conditions. Sato also believed that the 15th Army was making no real attempt to provide for the delivery of supplies to his division. He therefore started to withdraw his troops to conserve their strength, thus allowing the British to secure Kohima Ridge.
On 25 May, Sato notified the 15th Army's headquarters that the 31st Division would withdraw from the Kohima area on 1 June unless it received supplies. Finally, on 31 May, Sato ordered the abandonment of the Naga Village and other positions to the north of the road despite Mutaguchi’s orders that they were to be held: Sato’s unilateral decision to withdraw his division was an event which had not even been considered by the Japanese army up to this time, and was deemed a major affront to Mutaguchi and the high command. Sato’s withdrawal had the immediate effect of allowing the Indian XXXIII Corps to outflank the position of Miyazaki’s Left Assault Force on the Aradura Spur and begin its push to the south.
The Left Assault Force nevertheless continued to fight rearguard actions and demolish bridges along the road to Imphal, but was eventually driven off the road and forced to retreat toward the east. The remainder of the Japanese division retreated painfully toward the south, but found very little to eat, as almost all of what little supplies had been brought forward across the Chindwin river had been eaten by other Japanese formations and units, which were just as starving as Sato’s men.Many of the 31st Division's men were now too weak to drag themselves any farther to the south than Ukhrul, near the site of the Battle of Sangshak, where hospitals had been established, though without medicines, medical staff or food, or Humine some 20 miles (32 km) to the south of Ukhrul, where Sato again hoped to find supplies but was once more denied.
The Indian XXXIII Corps followed in the wake of the retreating remnants of the 31st Division. The British 2nd Division advanced along the main road, while the Indian 7th Division, which was reliant largely on Jeeps and mules for its logistical requirements, moved through the rough terrain to the east of the road. On 22 June, the leading troops of British 2nd Division met the main body of Indian 5th Division, which was advancing to the north from Imphal, at Milestone 109, some 30 miles (48 km) to the south of Kohima. The siege of Imphal was now over, and truck convoys quickly carried heavy loads of vital supplies to the formations and units at Imphal.
During the Battle of Kohima, the British and Indian forces lost 4,064 men killed, wounded or missing, and the Japanese had suffered 5,764 battle casualties in the area of Kohima area, and many of the 31st Division's survivors subsequently died of disease or starvation.
Having ignored the 15th Army's orders for several weeks, Sato was removed from command of the 31st Division on 5 July. After his removal from command, Sato refused an 'invitation' to commit ritual suicide and demanded a court martial to clear his name and to make public his complaints about the headquarters of the 15th Army, but in response to prompting by Kawabe, doctors declared that Sato had suffered a mental breakdown and was unfit to stand trial. Sato was replaced in command of the 31st Division by Lieutenant General Tsuchitaro Kawata. Miyazaki was promoted to lieutenant general and appointed to command the 54th Division in Arakan.
While 'U' (ii) did succeed in delaying the planned British 'Capital' offensive to the line of the Chindwin river and then across it to Mandalay, the huge losses the Japanese suffered in the Battles of Imphal and Kohima, most of them as a result of starvation and disease, effectively crippled their defence of central and northern Burma against Allied attacks during the following year, and most especially the 'Extended Capital' upgraded version of 'Capital'.
On the Allied side, Grover was dismissed from command of the British 2nd Division on 5 July, for perceived slowness in conducting the offensive, and also after complaints about his handling of Indian units, especially the 33rd and 161st Brigades, attached to his division. His successor was Major General C. G. G. Cameron. The commander of the Indian 161st Brigade during the siege, Warren was promoted to command the Indian 5th Division but was killed in an air crash the following year.
During the sieges of Kohima and Imphal, the Allies relied entirely on resupply from the air by British and US aircraft operating from India until the road from the railhead at Dimapur had been cleared. At Kohima, as a result of the narrow nature of the ridge lines, accuracy in the dropping of air-delivered supplies proved to be a major problem and, moreover, as the fighting intensified and size of the British and Indian defended area decreased, the task became still harder and more dangerous.
The increasing dominance of Allied air power by this stage of the Burma campaign was a major factor in helping the Allies turn the tide of the war in this theatre. Allied air supply enabled British and Indian troops to hold out in positions that they might otherwise have had to abandon due to shortages of ammunition, food and water, as reinforcements and supplies could be brought in even when garrisons were surrounded and cut off.