Operation B (iii)

'B' (iii) was the Japanese seizure of Burma (15 January/31 May 1942).

Burma came under British control in 1886, and as a country has a population which is ethnically very diverse. These different groups chose opposing sides when the Japanese invaded Burma in January 1942. The ethnic Burmese inclined towards the Japanese, who had enticed them with promises of independence, until the Japanese promises began to ring hollow later in the war. The Shan tribes of eastern Burma were strongly pro-Japanese, while the hill tribes of the north in general, and especially the Kachins, were strongly pro-British, and this tendency was later increased by Japanese atrocities. The total population in 1941 was about 18 million, and of these, about a million were Indians who dominated the commercial and civil service sectors. The rest of the population comprised 10 million Burmans, 4 million Karens, 2 million Shans, and about 1 million hill tribesmen.

Burma has an area of 261,227 sq miles (676578 km˛) and extends over 20° of latitude. The geography is dominated by the Irrawaddy river valley, which is a low plain in the central part of the country, and the bulk of the population is located along this valley. The other three major rivers are the Chindwin to the west of the Irrawaddy, and the Sittang and Salween to the east of it: these other three rivers also flow basically from north to south. The area around Mandalay is surrounded by mountains whose rain shadow creates a dry belt, which receives just 40 in (1000 mm) of rainfall per year. The remainder of Burma comprises rugged, jungle-clad hills subject to extremes in climate as a result of the shifting monsoon periods: during the winter, the country is hot, dry and dusty, but in the summer, between the middle of May to the middle of October, it becomes a sweltering, humid sea of mud.

Burma also includes the Tenasserim, the narrow appendix of coast extending along the western side of the Kra isthmus. This region had a series of airfields which were vital elements of the British air bridge between India and Malaya. The Tenasserim area also included useful ports at Tavoy and Moulmein.

Though much of the Burmese economy was based on rice and timber (with rice exports, mostly to India, totaling 3.5 million tons per year), the Irrawaddy valley contains significant oilfields such as those at Yenangyaung. There is also considerably mineral wealth in the form of tin and tungsten mined in the mountains running along the eastern boundaries of the country and down to the Kra isthmus. Total tin production in Burma reached nearly 6,000 tons per year by 1939. There were also significant manganese deposits at Tagaung Taung. The Japanese desired these mineral resources, but their primary objective for the seizure of Burma was strategic: the country would form the western linchpin of the defence perimeter they planned to establish, and also serve as a possible staging area for an invasion of India.

Another strategic motive for the Japanese invasion of Burma was the severance of the Burma Road along which China received the bulk of its Lend-Lease aid. The Allies later expended considerable resources in the restoration of the land route to China by taking northern Burma and constructing a new road from Ledo in India through the jungles to China. This road was completed in 1945, by which time it had become largely irrelevant to the outcome of the war.

The pre-war and early war plans of the UK for the defence of its Far Eastern possessions involved the construction of a series of airfields to provide a secure air link between Singapore and Malaya in the south-east with India in the north-west. These plans had not taken into account the fact that the UK was also at war with Germany, which consumed by far the largest part of the available British resources, so when Japan entered the war in December 1941 the British and commonwealth forces needed to defend these possessions were just not available. Moreover, in the period before the war Burma had come to be seen as militarily unimportant in itself, and therefore an unlikely target for Japanese aggression.

Thus Lieutenant T. J. Hutton, commanding the Burma Army headquartered in Rangoon, had only Major General J. G. Smyth’s Indian 17th Division and Major General J. Bruce-Scott’s 1st Burma Division for the defence of this British colony, although help was expected from the Chinese Nationalist government under Generalissimo Chiang Kai-shek as the only route by which China could receive outside support passed largely through Burma.

During the war, the Indian Army was expanded more than 12 times from its peacetime strength of 200,000, but late in 1941 this expansion was still in its early stages, so most units lacked all but the most rudimentary training and the barest levels of weapons and other equipment. Moreover, the training and equipment that most Indian units in Burma had received when they were committed to the Burma campaign had been designed to prepare them for operations in the dry heat of the Western Desert campaign or along the North-West Frontier of India, and not the humid jungles of Burma in which much of the early fighting took place.

Originally raised for the internal security role, the battalions of the Burma Rifles which constituted the main strength of the 1st Burma Division had also had been rapidly expanded, comprised mainly recruits with limited training, and these too were short of equipment.

Japan entered the war primarily to obtain raw materials, especially oil and other strategic commodities, from the European (and most especially Dutch) possessions in South-East Asia: all of these possessions were held only weakly because of the colonial powers' greater commitment to the war in Europe. Japanese plans involved an attack on Burma partly as the country also possessed natural resources (oil from fields around Yenangyaung, minerals and large surpluses of rice), partly to protect the western flank of their main attack against Malaya and Singapore, and partly to provide a buffer zone shielding the territories they intended to occupy. Another factor in Japanese considerations was the Burma Road: completed in 1938, this linked Lashio at the head of a railway from the port of Rangoon with the Chinese province of Yunnan. This newly completed link was being used to move aid and munitions to the Chinese Nationalist forces that had been fighting the Japanese for several years, and the Japanese naturally wished to cut this link.

Lieutenant General Shojiro Iida’s 15th Army was assigned the twin missions of occupying northern Thailand, which had signed a treaty of friendship with Japan on 21 December 1941, and attacking the southern Burmese province of Tenasserim. The army consisted initially of Lieutenant General Shozo Sakurai’s first-class 33rd Division and Lieutenant General Hiroshi Takeuchi’s 55th Division, but each of these formations was weakened for several weeks by detachments to other operations. Thai troops would also aid, although only to a very limited degree, in the invasions of Burma and Malaya.

The first Japanese attack materialised on 15 January 1942, when a detachment of the 15th Army) crossed the Isthmus of Kra from Chumphon on the Gulf of Siam and attacked Victoria Point, almost the most southerly point of Burma on the Andaman Sea. The attack had been expected and was not contested. The second attack was a small probing raid directed at a police station in southern Tenasserim, and was driven back. The 55th Division's 143rd Regiment then launched overland attacks on the airfields at Tavoy and Mergui in Tenasserim, the southern 'appendix' of Burma. The defence of these strategically important airfields offered the British considerable problems, principally as the area was very difficult to reinforce, but the Burma Army had nevertheless been instructed to hold them because of their importance to the defence of Malaya, which would otherwise be cut off except by sea. The Japanese forced their way over the steep jungle-covered mountains of the Tenasserim range, and attacked Tavoy on 18 January. The defenders, the 3 and 6/Burma Rifles, were overwhelmed and forced to evacuate the town in disorder. Located farther to the south, Mergui was evacuated before it was attacked.

Rangoon was initially defended relatively successfully against Japanese and Thai air attacks by small RAF detachments reinforced by a squadron of Colonel Claire L. Chennault’s 1st American Volunteer Group detached from bases in south-western China. The majority of the airfields in southern Burma were located between Rangoon and the 15th Army's advance, and as the Japanese gained use of the airfields in Tenasserim, the warning time available to the air defence of Rangoon was steadily shortened, thereby rendering increasingly difficult the protection of Rangoon against air attack.

On 22 January 1942, the main body of the 55th Division began the principal Japanese attack westward from Rahaeng in Thailand across the Kawkareik Pass toward the important city of Moulmein. Brigadier J. K. Jones’s Indian 16th Brigade of the Indian 17th Division, guarding this approach, retreated hastily to the west. The Japanese division advanced to the mouth of the Salween river at Moulmein, which was garrisoned by Brigadier A. J. H. Bourke’s 2nd Burma Brigade. The position was almost impossible to defend, however, and moreover the Salween river, almost 1.5 miles (2.4 km) wide, lay behind it. The 2nd Burma Brigade was steadily compressed, and eventually had to retreat across the river by ferry on 31 January after abandoning large quantities of supplies and equipment. Some 600 men were left behind in Moulmein, and only a few of these managed to swim the river.

The Indian 17th Division pulled back to the north, and next attempted to hold the Bilin river. Smyth sent one of his senior subordinates, Brigadier D. T. Cowan, to Rangoon to ask Hutton for permission to fall back to the Sittang river, but Hutton refused any such authorisation. The Indian 17th Division held at the Bilin river for two days of close-quarter jungle fighting, but the Japanese made clever use of outflanking tactics and, with encirclement of the division imminent, Hutton arrived from Rangoon and gave Smyth permission to fall back. The Indian 17th Division disengaged under cover of darkness and began a 30-mile (48-km) retreat along the dusty track to the major bridge over the Sittang river.

The battle for the Sittang bridge took place on 19/23 February. The bridge was of steel construction and spanned several hundred yards of the Sittang near this river’s estuary on the southern coast of Burma. The Indian 17th Division had given its all in the fighting for the Bilin river, was already debilitated and now, weakened and in retreat, it received permission on 19 February to withdraw to and then across the Sittang as the 214th and 215th Regiments of the 33rd Division advanced with the object of catching the Indian 17th Division on the eastern bank of the river and cutting it off. The Indian 17th Division pulled back to a succession of fallback lines, but had too few men to prevent the Japanese from outflanking it whenever it tried to halt. The division eventually retreated toward the bridge over the Sittang river in general disorder.

The retreat was delayed by incidents such as a vehicle breaking through the bridge deck, air attacks (including, allegedly, accidental attacks by the RAF and American Volunteer Group) and Japanese harassment. It was bright and hot on 21 February, and the Indian 17th Division was short of water. Japanese aircraft strafed and bombed the Indian troops on the road, inflicting serious casualties and forcing them to abandon vehicles and equipment, and many men took cover in a nearby rubber plantation. At 05.00, the divisional headquarters came under attack at Kyaikto, but the Japanese were beaten back.

A small force made up of detachments from several different units (including the Duke of Wellington’s Regiment) defended the bridge, but Jones’s Indian 16th Brigade and Brigadier R. G. Ekin’s Indian 46th Brigade were still farther to the east and cut off. Fearing paratroop landings, Smyth deployed the 1/4th Gurkha Rifles to the western end of the bridge to hold it against attacks from the rear while the Indian 17th Division crossed. He was obliged to send them back again when the Japanese attacked from the east and, in their first assault, nearly took the eastern end of the bridge. The 3rd and 5th Gurkha Rifles, approaching the bridge from the east, were driven off in severe fighting. There followed as period of intense jungle fighting that lasted for most of the day. The bridge was again nearly taken, but the Japanese were again beaten back.

At dusk on 21 February, the Indian 17th Division still held the bridge, which Smyth had ordered his engineers to prepare for demolition. Early in the morning of 22 February it became clear that the Japanese might take the bridge within the hour, and Smyth’s choices were now either to destroy the bridge, stranding more than half of his own troops on the wrong side of the river, or to let it stand and give the Japanese a clear march to Rangoon. He decided the bridge must be destroyed, and this was done at 05.30 on 22 February. The Japanese could now have destroyed the Indian 17th Division but, wishing to take Rangoon as rapidly as possible, opted not to lose time by becoming involved in mopping-up operations.

The Japanese therefore disengaged and headed north along the eastern side of the Sittang river in search of another crossing point. Thus, later on 22 February, survivors of the Indian 17th Division were free to swim or ferry themselves over the Sittang river in broad daylight.

As the Sittang river was not, in itself, a major obstacle to the Japanese advance, it is arguable that more harm than benefit resulted from the destruction of the bridge as this stranded two Indian brigades and delayed the Japanese capture of Rangoon by 10 days at most. Fortunately for the survivors of Indian 17th Division, the Japanese dismantled their roadblocks, so the Indian troops who had escaped the Sittang bridge disaster were able to slip away to the north.

The Indian 17th Division’s infantry manpower after the Sittang battle was just 3,484, slightly more than 40% of its establishment, though it was already well below strength even before the start of the battle. Most of the divisional artillery, vehicles and other heavy equipment were lost. Between them, the division’s men had only 550 rifles, 10 Bren light machine guns and 12 sub-machine guns, and most of the men had lost their boots while swimming the river.

Though the Sittang was in theory a strong defensive position, the disaster at the bridge left the Allied forces too weak to hold the line of the Sittang, but General Sir Archibald Wavell, heading the ABDA Command, nevertheless ordered that Rangoon should be held, for the Burma Army was due to receive substantial reinforcements, including an Australian division, from the Middle East. On 28 February, Wavell formally relieved Hutton, who had officially already been superseded in command by General the Hon. Sir Harold Alexander, and on the following day also replaced Smyth, who was in any case very ill, with Cowan at the head of the Indian 17th Division, which survived as a cohesive formation and was later replenished, re-equipped and rebuilt.

Although the Australian division never arrived in Burma, some reinforcements, including Brigadier J. H. Anstice’s British 7th Armoured Brigade, did land in Rangoon. Alexander ordered counterattacks, and a defensive position was created at Pegu, to the north-east of Rangoon on the railway line connecting the Burmese capital and Mandalay away to the north up the Sittang river. With the Indian 17th Division decimated and scattered, the entire force available for the whole of Burma was the 1st Burma Division and the 7th Armoured Brigade, equipped with US-made M5 Stuart, or 'Honey', light tanks.

The result was the battle of Pegu, which was fought on 3/7 March. B Squadron of the 7th Hussars reached the village of Payagyi to find the Japanese already there. The visibility was poor, and radio communication difficult. After a brief infantry engagement, the 'Honey' tanks opened fire, destroying two Type 95 tanks. In the confused fighting which followed, two more Type 95 tanks were destroyed, another Type 95 was abandoned by its crew, and four Japanese anti-tank guns were captured. Then the order came for the British to move to Hlegu. This was also found to be in the hands of the Japanese, who had erected a roadblock that they defended with 'Molotov cocktails', knocking out one of the 'Honey' tanks, before being forced to retreat by the fire of the tanks' 37-mm guns.

By this time Alexander had realised that Rangoon could not be retained, and now implemented a scorched earth plan to deny the Japanese the use of Rangoon’s facilities: after the port had been destroyed and the oil terminal blown up, the city was abandoned in flames. Alexander planned a 200-mile (320-km) withdrawal to the north-west across country to the Irrawaddy river at Prome.

But the objective of the fighting around Pegu, to convince the Japanese that Rangoon would be defended, had been achieved. At about 12.00 on 8 March the 215th Regiment entered Rangoon, and was much surprised to discover that there was no defence. Sakurai immediately ordered the 215th Regiment to pursue the retreating British column, which he now realised was the whole of the British strength from the Rangoon area. The remnants of the Burma Army faced encirclement as they retreated north-west from the city, but broke through the roadblock at Taukkyan on 7/8 March as a result of a mistake by Colonel Takanobu Sakuma, commander of the 214th Regiment. Sakuma had been ordered to block the main road north from Rangoon while the main body of the 33rd Division passed round Rangoon to attack from the west.

Taukkyan was a village on a junction at which the road north from Rangoon toward Prome met the road east to Pegu, the latter being strategically located to cover Rangoon from an attack from the east. Early in 1942, therefore, it had been garrisoned by troops of Brigadier H. Hugh-Jones’s Indian 48th Brigade. But this force had been outflanked by a Japanese attack, and was now surrounded. On 6 March men of the 1/11th Sikh Regiment were despatched north from Rangoon to relieve Pegu, but stopped part of the way there to take up a defensive position on the road linking Taukkyan and Pegu after reports of extensive Japanese infiltration. The battalion held this position overnight and, early on 7 March following the battle of Pegu, the survivors of the garrison pulled out of Pegu and fell back through their lines. That evening, the battalion then withdrew toward Taukkyan.

On 6 March, meanwhile, Alexander had made his decision to abandon Rangoon and march north toward Prome. As noted above, the Japanese had moved round the forces on the Pegu road and established a strong block on the road at Taukkyan. As a result, the whole of the Burma Army, including the army headquarters, surviving strength of the Indian 17th Division and 7th Armoured Brigade, were caught in the Rangoon area, unable to retreat to the north. So the block had to be cleared. The first attack, on 7 March, was made by a troop of the 7th Hussars' M3 tanks, with infantry support, but was driven off by the Japanese with the loss of one tank and heavy infantry casualties. A second attack was then made by a squadron of the 2nd Royal Tank Regiment with artillery support, and by the 1/Gloucestershire Regiment, but this too was unsuccessful. The final attack that day was made by two companies of the 2/13th Frontier Force Rifles, and again failed. The surviving forces withdrew to establish a defensive perimeter for the night, during which the Japanese launched a heavy counterattack. But the Indian battalion was still holding its position on the following morning.

The only fresh troops available were the men of the 1/11th Sikhs, pulling back from Pegu, and the 1/10th Gurkhas. A plan was drawn up for these two battalions, backed by artillery and supported by one squadron of the 7th Hussars and a detachment of the Burma Military Police attached to the 1/Glosters, to attack the block at 08.45 on 8 March. As they moved into position, the Sikhs were attacked by Japanese aircraft, taking severe casualties; the Gurkhas, meanwhile, lost their way to the forming-up area and did not arrive in time. The artillery barrage also failed to materialise, but the 1/11th Sikhs and 7th Hussars moved toward the block with the Sikhs breaking into an unexpected bayonet charge. The small Japanese garrison immediately abandoned the block and fled, leaving the British forces in control without any significant resistance. The Japanese launched a small counterattack in about platoon strength, with air support, shortly after the Sikhs had occupied the block, but were quickly repelled, and this marked the limit of the Japanese response.

It later emerged that Iida had anticipated that the British would stand and fight in Rangoon, and had accordingly ordered the 33rd Division, the formation moving against the city, to push forward with speed rather than to try to surround the city. As a result, while a strong block had initially been laid at Taukkyan, this had been designed only to protect the division’s flanks: once the division had passed through and was marching on Rangoon, the garrison had been radically reduced. The first of the Burma Army’s rear-area units passed through the block shortly after it had been secured, and the convoys continued until about 12.00, at which time the bulk of the Burma Army had been fully evacuated.

The combat units withdrew through Taukkyan at about 16.30, and the Sikh rearguard moved north at 18.00.

After the fall of Rangoon, the Allies had decided to make a stand in the north of Burma. It was hoped that the Chinese Expeditionary Force in Burma (Lieutenant General Tu Yu-ming’s 5th Army and Lieutenant General Kan Li-chu’s 6th Army in the Sittang and Salween river valleys respectively, on a level with Taunggyi, with Lieutenant General Chang Chen’s 66th Army farther to the north near Lashio, the southern terminus of the Burma Road) could help check the Japanese advance. Each of these Chinese armies had approximately the strength of a British division, but with comparatively little equipment. Supplies were not a major concern, if only in the shorter term, as much matériel (including large quantities originally meant for onward transmission to China) had been evacuated from Rangoon, rice was plentiful, and the oilfields in central Burma were still intact. It was clear, though, that in the longer term only the recapture of Rangoon would allow the Allies to hold Burma indefinitely.

At this stage of the campaign, the Allies hoped that the Japanese advance would slow, but in fact it gathered pace as the Japanese now used their possession of Rangoon to reinforce their two divisions in Burma by shipping in Lieutenant General Renya Mutaguchi’s 18th Division from Malaya after the fall of Singapore, and Lieutenant General Masao Watanabe’s 56th Division from the Netherlands East Indies after the fall of Java: the 18th Division moved to the north along the Sittang river valley and replaced the 55th Division as the Japanese spearhead in the area north of Pyinmana, and the 56th Division deployed into the Salween river valley and headed to the north toward Taunggyi and Lashio. The two new divisions also brought with them large numbers of captured British trucks and other vehicles, which allowed them to move supplies rapidly using southern Burma’s road network, and also to start to make use of motorised infantry columns, particularly against the Chinese forces.

The Allies were also harassed by the rapidly expanding anti-British Burma Independence Army, and were hampered by large numbers of refugees (mostly Indian civilians), the progressive breakdown of the civil government in the areas they held, and the rate of desertion from the Burma Rifles. The RAF wing operating from Magwe was crippled by the withdrawal of the radar and radio intercept units to India and the Japanese soon gained supremacy in the air.

The British had created Lieutenant General W. J. Slim’s Burma Corps to relieve the Burma Army of the need to conduct the day-to-day business of operations. Slim tried to mount a counter-offensive on the western part of the front, where the 33rd Division was moving to the north along the Irrawaddy river valley in the direction of Magwe and also striking out to the west in the direction of the Arakan coast, but the troops were repeatedly outflanked and forced to fight their way out of encirclement.

The Burma Corps was gradually pushed northward in the direction of Myangyan and Mandalay after losing two of the most important battles of this phase of the Japanese conquest of Burma. These were the battle of Toungoo in the Sittang river valley on 24/30 March, and the battle of Yenangyaung in the Irrawaddy river valley on 11/19 April.

On 8 March, the day of Rangoon’s fall, advanced elements of Major General Dai An-lan’s 200th Division of the Chinese 5th Army arrived in Toungoo, a key location whose defence the Chinese assumed from a small British detachment. Toungoo controlled the road north toward Mandalay and the bridge over the Sittang river that carried the road east to the Karen States and north to Loikaw, the Shan States, Lashio and the Chinese province of Yunnan. Capture of the city could threaten the flank of the Allied defensive line in Burma and open the way to a Japanese advance into central Burma. Dai decided that the city of Toungoo itself would be the main defensive position of the Chinese forces, with an outpost line farther to the south at Oktwin. He sent his Motorised Cavalry and 1st Company, 598th Infantry, to the banks of the Kan river 35 miles (56 km) to the south of Toungoo and 12 miles (19 km) to the south of Pyu. The cavalry regiment and a company of infantry pushed up to the Kan river, a platoon of cyclists taking up position near the bridge over the Sittang river. They were to delay the advance of the Japanese until the defences at Toungoo were complete.

Meanwhile the men of the 200th Division began digging in within the old city walls and along the advanced line at Oktwin. Toungoo itself was divided into the new town east of the railway and the old town west of it. The old town had a well preserved ditch and fortified wall which provided a good defensive position for the Chinese. The Chinese then enhanced the defences with carefully concealed positions built of local timber. To make things more difficult for the attackers the land around Toungoo was flat and featureless, except for the Sittang river to the east.

Some 10 days later, on 18 March, the first skirmish with the leading elements of the 55th Division began on the Kan river. Falling back over the next three days, the Chinese cavalry delayed the Japanese advance while the Chinese completed their defences at Oktwin and Toungoo. When the Japanese attacked Oktwin they were held for another two days by determined Chinese resistance. On 24 March, the 112th Regiment made frontal attacks on the Oktwin positions while the 143rd Regiment, with the aid of friendly local Burmese, made use of the cover of the jungle and wooded area to the west of the city in order to advance 2.75 miles (6 km) to the north and attack Toungoo airfield and a nearby railway station. This area was defended by only an engineer battalion, whose commander pulled back his men in panic.

This cut the 200th Division’s communications to the north, and left it encircled on three sides. Dai abandoned the outlying positions to concentrate his defence near the city walls of Toungoo: the 598th, 599th and 600th Regiments defended the northern, southern and western parts respectively. The divisional headquarters was relocated from the city to the eastern bank of the Sittang to avoid Japanese air and artillery attacks, and also to safeguard the remaining supply route to the east. Elements of a so-called Replacement Regiment, which had arrived during the previous day, were posted on the eastern bank of the Sittang, and extended the positions to cover the remaining lifeline of the division as well as the divisional headquarters.

At 08.00 on 25 March the Japanese launched an all-out attack on all three sides of the city with its 143rd Regiment on the left, 112th Regiment on the right, and 55th Cavalry plus a company of infantry along the Sittang. The Japanese plan was to drive the Chinese forces against the Sittang river, where they would be destroyed. Despite local penetrations in the north-western part of the defensive perimeter, the Japanese made no major progress as a result of heavy Chinese resistance until 22.00 when Japanese troops infiltrated Chinese positions in the north-western part of the Toungoo citadel, the breakthrough element soon being followed by a full battalion. The Chinese reinforced the 600th Regiment with the 2/598th Regiment and counterattacked. There was severe house-to-house fighting and the lines between the forces were so close that Japanese air and artillery support found it difficult to avoid hitting their own men. The Chinese counterattack failed to recover the lost positions when Japanese troops made good use of the buildings and the stone walls around a local cemetery. The 600th Regiment was moved back between the other two regiments to defend Toungoo city itself. Elsewhere the bridge over the Sittang river became the target for Japanese firepower and was so severely damaged that vehicles could no longer cross it.

The Japanese attacks continued on 26 March, when the 112th Regiment attacked and took the south-western corner of Toungoo but was then prevented from making further progress. On the left, a flanking move to attack the north-western part of Toungoo was no more successful. The 55th Cavalry Regiment's attack was also repulsed. The Chinese launched counterattacks against the 112th Regiment and 55th Cavalry Regiment with about 300 men in each sector, but these were repulsed. By the evening, the Japanese had taken that part of the city to the west of the railway, while the Chinese held on to the main part of the city to the east of the railway. The two sides faced each other across the railway at a distance of less than 100 yards (90 m), making it difficult for Japanese to use air and artillery support. Eventually the Japanese withdrew some 200 yards (185 m) to allow their warplanes and guns to operate effectively. During the bombardment the Chinese hid in their camouflaged positions then held their fire until the Japanese advanced and were within 40 to 50 yards (35 to 45 m) and then opened up on them with machine guns and grenades. This happened repeatedly, and by the end of the day the 200th Division had taken very heavy losses, but at the same time inflicted so many casualties that the Japanese were finding it hard to continue their frontal attacks.

The arrival of Major General Liao Yao-hsiang’s New 22nd Division to the north of Yedashe forced the Japanese to send the 2/143rd Regiment to Nangyuen in order to prevent the Chinese reinforcements from reaching Toungoo. This considerably reduced the strength available for Japanese attacks. The third regiment of the 55th Division's three-regiment 55th Infantry Group, namely the 144th Regiment, as well as a battalion of artillery and a company of cavalry, were not with the division in the battle of Toungoo, with the result that the division lacked sufficient strength and the attack consequently stalled. On 27 March there was a lull in the fighting during the morning, but Japanese warplanes came back in the afternoon and systematically bombed and strafed the Chinese positions. The Japanese continued to press their attacks with this air support, and in the afternoon fired large numbers of tear gas shells. Despite all this, the Chinese held their ground. It was then decided to await the arrival of the 3rd Heavy Field Artillery Regiment, equipped with 150-mm (5.91-in) howitzers, before resuming attacks on the Chinese positions on 28 March.

On this day the 3rd Heavy Field Artillery Regiment arrived and, with strong artillery support as well as bomber and tear gas attacks, the Japanese inflicted heavy casualties on the Chinese. The right wing of the attack managed to destroy many Chinese strongpoints with artillery support. However, the light bombers did not arrive until 15.00 as a result of fog over their airfields, and it was not possible to overcome the stubborn Chinese resistance, which had considerable depth, even though the fighting lasted into the evening. Meanwhile, the 56th Reconnaissance Regiment of the 56th Division, comprising two motorised infantry companies and a machine gun company, a company of mountain guns and a platoon of engineers, was moving rapidly north from Rangoon in a column of 45 trucks with a company of six armoured cars, totalling 404 men. This force made rapid progress along the main road to Toungoo and reached the headquarters of the 55th Division by 12.00 on 28 March. It was decided to move this force to the east of the Sittang river in order to attack the rear of the Chinese positions. Crossing at 20.00 on the same day, the fresh force forded the Sittang river at Wagyi, just south of the city, where the water was only chest high, leaving its vehicles behind. If the Japanese attack to the east of the Sittang river was successful, the whole of the 200th Division would be encircled. The divisional commander personally organised the defence, and two companies of the 3/598th Regiment were ordered to attack the exposed left flank of the Japanese. Severe fighting continued within Toungoo. Around the divisional headquarters on the eastern bank, the fighting inflicted heavy losses on the 3/599th Regiment as well as the divisional support company, but the Chinese were nonetheless able to hold their ground. On 29 March the 55th Division used its last strength for yet another attack with the support of all available guns. By 12.00 the troops on the left were able to advance into the north-western part of the city, and the escape route of the Chinese was threatened.

Covered by the fight to the west, the 56th Reconnaissance Regiment moved to the north and attacked the Chinese flank guard east of the river, and by 12.00 on 29 March had overrun it, so threatening the Chinese divisional headquarters and the Sittang river bridge. During the afternoon of 29 March the 200th Division received orders for the whole formation to pull back during the evening, first toward the east and then to the north along the eastern bank of the Sittang river. Fighting in the city continued into the dark with the city on fire. The Chinese continued to resist stubbornly and the Japanese made no further progress. By 22.00 the 56th Reconnaissance Regiment had closed on the Sittang river bridge, and finally noted signs of wavering in the Chinese forces as night fell. However, this was the Chinese withdrawal. Dai instructed each Chinese battalion leave a rearguard which launched night attacks to cover the withdrawal of the main force. The retreat was led by the 599th Regiment crossing the battered and threatened bridge followed by the 600th Regiment, and then the 598th Regiment forded the river. By 04.00 the entire 200th Division had moved out of Toungoo in good condition, taking all its wounded. The Chinese claimed that their rearguards left before dawn.

On the morning of 30 March the 55th Division attacked all along the front claiming heavy resistance, despite withdrawal of most if not all of the Chinese. After engineers managed to blow up Chinese positions and strongpoints at 08.50, the men of the 55th Division finally broke through and linked with the troops of the 56th Division who had seized the vital bridge over the Sittang river at 07.00 and then attacked Toungoo from the east. This ended the battle, leaving the Japanese in possession of the city and bridge over the Sittang river.

The road to the east was open for the Japanese to use as a means of outflanking the left of the Allied line in Burma. Sent south to support the 200th Division, the New 22nd Division had meanwhile advanced as far as far Nangyun railway station, and partially dislodged the 2/143rd Regiment. The division had also sent patrols farther south toward Toungoo, threatening the Japanese flank and rear. The retreating 200th Division joined the New 22nd Division at Yedashe after withdrawing to the north along the eastern bank from Toungoo, crossing the Sittang river to the east of Nangyun. The Chinese then withdrew to new defensive positions at Yedashe in their attempt to block the Japanese advance up the Sittang river valley.

But after the fall of Toungoo, the road was open for the motorised troops of the 56th Division to shatter the Chinese 6th Army to the east in the Karen States and advance north through the Shan States to capture Lashio, outflanking the Allied defensive lines and cutting off the Chinese armies from Yunnan. With the effective collapse of the entire defensive line, there was little choice left other than an overland retreat to India or to Yunnan. Away to the north-west, meanwhile, the battle for the Yenangyaung oilfields started on 11 April and continued for a week.

The Japanese attacked Hugh-Jones’s Indian 48th Brigade at Kokkogwa at night in a storm, and on the following day the 2nd Royal Tank Regiment was in action near Magwe, and at Thadodan and Alebo. Between 13 and 17 April the British fell back, and on several occasions Japanese roadblocks split the Burma Frontier Force, 1st Burma Division, headquarters of the 7th Armoured Brigade and 2nd Royal Tank Regiment into three forces. The situation became so critical that Alexander asked Lieutenant General Joseph W. Stilwell, the field commander of the Chinese forces in Burma, to move Major General Sun Li-jen’s New 38th Division as rapidly as possible into the Yenangyaung area. On 16 April almost 7,000 British soldiers, together with 500 prisoners and civilians, were encircled by an equal number of men of the 33rd Division at Yenangyaung and its oilfields. The Japanese formation had cut the Magwe road between Slim’s two divisions, which were now about 50 miles (80 km) apart, and Scott of the 1st Burma Division asked Sun for assistance soon after his new 38th Division had entered Burma from China. Sun requested authorisation to lead the whole of his New 38th Division to Yenangyaung, but the Lieutenant General Lo Cho-ying, commanding the 1st Route Expeditionary Force, refused and so, on 17 April Sun led the 113th Regiment with only 1,121 men on the rescue mission.

Because the Chinese had none of their own artillery or tanks, Slim supported them with the tanks and 25-pdr guns of Anstice’s 7th Armoured Brigade. For the next three days the Chinese and British force attacked to the south. Meanwhile, the 1st Burma Division fought its way to and across the Pin Chaung river where they met the relief column on 19 April. On the next day the Allied force again attacked to the south toward Yenangyaung and Pinchaung, where the Japanese suffered heavy casualties as the relief force reached the 1st Burma Division’s pocket. But the Allied force was too weak to hold the oilfields and had to retreat north after losing almost all of its equipment and its cohesion. The retreat was undertaken in dreadful conditions, for in addition to comparatively small bodies of cohesive troops trying to save as many of themselves and as much of their equipment as possible, there were large numbers of disorganised stragglers, wounded starving refugees and sick. The result was huge congestion on the primitive roads and tracks leading to India.

The Burma Corps retreated to Manipur in India, but most of this formation’s remaining equipment could not be ferried across the Chindwin river and was therefore lost at Kalewa, although the troops escaped a Japanese attempt to trap them at Shwegyin to the east of the river. The Burma Corps reached Imphal in Manipur just before the monsoon broke in May 1942, and its subordinate formations and units found themselves living out in the open under the torrential monsoon rains in extremely unhealthy circumstances. The army and civil authorities in India were very slow to respond to the needs of the troops and civilian refugees.

The headquarters of the Burma Corps was disbanded, and responsibility for the front with the still-advancing Japanese was allocated to the headquarters of Lieutenant General N. M. S. Irwin’s IV Corps, which had recently arrived in India. By this stage the British losses amounted to 13,463 men, while those of the Japanese were 2,143 men.

The British administration of Burma fell back to Myitkyina in the north of the country, accompanied by many British, Anglo-Indian and Indian civilians. While the governor and the most influential civilians were flown out from Myitkyina, together with some of the sick and injured, most of the other refugees were forced to make their way from Myitkyina to India via the unhealthy Hukawng valley and the forests of the precipitous Patkai mountains.

The Japanese advance had cut off many of the Chinese troops from China, so many of these also retreated via the Hukawng valley route and subsisted largely by looting, further increasing the misery of the refugees. The Chinese New 38th Division however, fought its way west across the Chindwin, arriving in India substantially intact although only after suffering heavy casualties. The remaining Chinese troops tried to return to Yunnan through remote mountainous forests, and many died on the way. The Chinese forces which had retreated into India were put under the command of Stilwell, who had also made his way to India on foot. After recuperating, these Chinese forces were re-equipped and re-trained by US instructors as the core of the Chinese Army in India (New 1st Army from February 1943).

The 18th and 56th Divisions thus pursued the Chinese into Yunnan, but were ordered to halt on the Salween river on 26 April. the 33rd Division likewise halted on the Chindwin river at the end of May, ending the campaign until the end of the monsoon rains.

In the Arakan coastal province, part of the Burma Independence Army reached Akyab island before the Japanese, and also instigated riots between the Buddhist and Moslem populations of the province. The Japanese advance in Arakan ended just to the south of the border with India, prompting the British military and civil authorities in and around Chittagong to implement a premature 'scorched earth' policy, which contributed to the Bengal famine of 1943.

In accordance with the terms of the military alliance signed between Japan and Thailand on 21 December 1941, meanwhile, the leading Thai elements of Lieutenant General Jarun Rattanakuln Seriroengrit’s Phayap Army crossed the border into the Shan States on 10 May 1942. The boundary between the Japanese and Thai operations was generally the Salween river, though the area of the Karen States was specifically retained under Japanese control. Lieutenant Colonel Thwuan Wichaikhatkha’s Cavalry Division, Major General Luang Phairirayordejd’s 2nd Division, Major General Phin Choonhavan’s 3rd Division and Colonel Luang Haansongkhram’s 4th Division of the Thai army, spearheaded by armoured reconnaissance groups and supported by the 90th Combined Wing of the Thai air force, engaged Major General Lu Kuo-chuan’s retreating Chinese 93rd Division, and took Kengtung, their main objective, on 27 May. Renewed offensives in June and November drove the Chinese back into Yunnan.