Operation Hai (iii)

'Hai' (iii) was a Japanese attempt to extricate Lieutenant General Shozo Sakurai’s 28th Army of General Heitaro Kimura’s Burma Area Army from the Pegu Yoma (Pegu mountain range) across the Sittang river into south-eastern Burma and western Thailand in the last major land battle fought by the Western Allies during World War II (2 July/7 August 1945).

The Japanese break-out from the Pegu Yoma and the Battle of the Sittang Bend were successive Japanese undertakings during the last weeks of the Burma campaign. Surviving elements of the Imperial Japanese army, totalling some 20,000 men retreating from western Burma, had managed to cross the Irrawaddy river to the east, but then become trapped in the Pegu Yoma before attempting to break out to the east in order to join other Japanese formations retreating from the British-led forces advancing to the south down the parallel Irrawaddy and Sittang rivers, and to the north-east from Rangoon. The break-out was the objective of Sakurai’s 28th Army with support at first from Lieutenant General Masaki Honda’s 33rd Army and later from Lieutenant General Shihachi Katamura’s 15th Army. Regrouping in Tenasserim after its retreat to the south along the eastern side of the Sittang river after 'Extended Capital' but now amounting to little more than one brigade in terms of its strength, as a preliminary the 33rd Army attacked the British positions in the bend of the Sittang river, near its mouth, in an unsuccessful distraction. The British knew that the break-out attempt was imminent, however, and their careful preparations resulted in the virtual annihilation of the Japanese forces involved, the Japanese suffering very heavy losses and the destruction of some formations and many units.

The Japanese lost about 14,000 men, significantly more than half of them killed, while the British-led forces suffered only 417 men (95 dead and 322 wounded). The break-out attempt and the battle which followed it was the last significant land battle of the Western Allied in World War II.

By a time early in 1944, the British-led forces in India had been reinforced and were able to operate on the basis of a much expanded and improved logistic infrastructure, which made it possible for them to contemplate an offensive deep into central Burma. The Japanese attempted to forestall this with the 'U' invasion of Assam in north-eastern India, but this resulted in the strategic and very costly defeat of Lieutenant General Renya Mutaguchi’s 15th Army in the Battles of Kohima and Imphal, and other setbacks in northern Burma. After another strategic defeat at the hands of Lieutenant General Sir William Slim’s British 14th Army in the Battles of Meiktila and Mandalay during 'Extended Capital', and the recapture of Rangoon in 'Dracula', the Japanese were further handicapped in their defence of Burma.

By this time the Burmese National Army under Aung San had switched sides to become the Burma Patriotic Army, and started to hunt and destroy Japanese patrols and also the foraging parties which were now essential to the effort of the remnants of Kimura’s Burma Area Army to survive in a situation in which Allied warplanes and warships dominated the air over and sea round Burma prevented the arrival of all but the most limited quantities of ammunition, fuel, food and medicine.

During April, Lieutenant General Sir Frank Messervy’s Indian IV Corps advanced 300 miles (480 km) from central Burma down the valley of the Sittang river. Japanese rearguards prevented them advancing all the way to Rangoon, the capital and main port of Burma, but on 2 May Rangoon fell to the 'Dracula' amphibious assault. On 6 May, the leading elements of Major General D. T. Cowan’s Indian 17th Division, which was spearheading the advance of the Indian IV Corps, linked with the troops who had carried out 'Dracula' at Hlegu, some 28 miles (45 km) to the north-east of Rangoon.

After the fall of Rangoon, the headquarters of the 14th Army moved to Ceylon to embark on the detailed planning of its planned recapture of Malaya and Singapore. For further operations in Burma, a new 12th Army headquarters was created, under the command of Lieutenant General Sir Montagu Stopford, out of the headquarters of what had been Stopford’s own XXXIII Corps. The 12th Army then assumed command over the Indian IV Corps in the Sittang river valley and directly commanded some divisions in the Irrawaddy river valley.

After retreating from Arakan and across the Irrawaddy river valley, the 28th Army had reached the Pegu Yoma, a range of low mountains, hills and uplands between the Irrawaddy and Sittang river valleys in central Burma. Here they were joined by Major General Hideji Matsui’s 105th Independent Mixed Brigade, also known as 'Kani' Force and created from men of anti-aircraft batteries, airfield construction battalions, naval anchorage units, NCO schools and the like, which had unavailingly faced the Indian IV Corps.

The Japanese trapped in the Pegu Yoma then prepared a major break-out operation to rejoin the Burma Area Army and escape into Thailand with it. The Sittang river was unfordable, and therefore as significant a military barrier to the Japanese as it had been in 1942 to the retreating British forces during the first Burma campaign of that same year. Kimura ordered Honda’s 33rd Army to cover this break-out by a diversionary offensive across the lower reaches of the Sittang river. In support, Lieutenant General Shihachi Katamura’s 15th Army was instructed to co-ordinate its effort with that of the 28th Army if the operation was failing to meet its objective.

British intelligence were aware of the Japanese intention to break out but lacked detailed information, so Stopford ordered the Indian IV Corps to spread itself over more than 100 miles (160 km) of front to block all possible Japanese escape routes . However, on 2 July a Gurkha patrol ambushed and wiped out a small Japanese force, in the process recovering a dispatch bag containing the complete operational plan for the Japanese break-out. he intelligence was quickly distributed among the British forces, which therefore had two weeks in which to prepare the destruction of the break-out. One of the intended Japanese routes of march lay directly across the Indian 17th Division’s headquarters at Penwegon, and Messervy reinforced this critical sector with Brigadier J. G. Flewett’s Indian 64th Brigade from Major General T. W. Rees’s Indian 19th Division.

The Japanese planned to advance to the Sittang river in three columns, under strict rules of engagement forbidding the use of firearms in favour of the bayonet and forbidding any radio communications once they had crossed the Sittang river on rafts, most of them to be made of bamboo. Sakurai underestimated the British strength arrayed against the remnants of his army, but believed he could get more than half his force across in fighting shape.

The 33rd Army attacked the Sittang Bend on 3 July in an attempt to aid the break-out effort. The attack was mistimed, however, as a result of the Burma Area Army's lack of any effective communications capability and took place a week before the 28th Army made its advance to the river. Under the temporary command of Lieutenant General F. I. S. Tuker from 14 July, the Indian IV Corps (Indian 5th, 17th and 20th Divisions and the Indian 255th Tank Brigade) allowed the advance of the Japanese, who were wholly unaware that their plans were known to the British, and then waited until many of the Japanese troops were in the exposed and fully targeted positions before unleashing a barrage of artillery fire and bombing. The artillery pounded the Japanese attack with the aid of forward observation officers who continually monitored Japanese movements and gave the signal to fire.

Royal Air Force 'cab rank' patrols of fighter-bombers under the control of visual control posts in the British forward positions to call down squadrons of Supermarine Spitfire and Republic Thunderbolt warplanes on known Japanese targets.

By 7 July Kimura was forced to order the 33rd Army, by now grievously hard hit, to halt any further operations, and then pulled it back while hoping that his army’s effort had been enough to facilitate the 28th Army's break-out, but the British knew of this and were already switching their attention to that sector.

Despite the mauling which the 33rd Army had suffered in its mistimed effort, on 15 July the 28th Army began its attempt to break though to the Sittang river with Lieutenant General Shigesaburo Miyazaki’s 54th Division in the north, Lieutenant General Ryozo Sakuma’s 55th Division in the centre with the headquarters of the 28th Army and the 105th Independent Mixed Brigade and Captain Fukami’s separate 13th Naval Guard Force in the south. Like the 33rd Army before it, the 28th Army was unaware of the fact that the British knew of its plan. By this time the monsoon was in full swing, and the British created two killing fields, the first for artillery targeting 12 Japanese crossing points along the highway, and the second for aircraft, which were able to operate even in these poor weather conditions, to attack those who managed to cross the road, especially in the area between the Sittang and Salween rivers. Forward observation officers were the keys to the success of the artillery and warplanes. Tanks and infantry, the latter both motorised and on foot, covered the gaps between the positions despite the heavy monsoon rains. The now pro-Allied forces of the Burma Patriotic Army were left to deal with any survivors on the eastern bank of the Sittang river.

The 55th Division ran straight into the Indian 19th Division’s strongpoint at Penwegon, and here the Indian formation’s tanks and infantry repelled every Japanese attack, inflicting huge losses in the process. Forward observation officers on the far side of the Sittang river continued to call down artillery fire on the Japanese as the survivors attempted to re-form and move to the south. The Japanese casualties were appallingly high in what was in reality a completely one-sided battle. The RAF also attacked troop concentrations and river craft of all kinds: it was discovered, when British and Burmese ground forces moved in, that Nos 273 and 607 Squadrons had killed about 500 Japanese in the village of Hpa-An. The remnants of the 55th Division did not reach the western bank of the Sittang river until 7 August.

Meanwhile the 600 men of the 13th Naval Guard Force broke out separately from the main body, largely as a result of the general confusion and numerous ambushes, and were effectively wiped out, only a handful surviving.

On 21 July the Japanese began their last and most desperate attempt to cross the Sittang river with their remaining 15,000 men, very large numbers of whom were sick. Having suffered heavily from cholera, dysentery and plague, the 54th Division emerged from the Pegu Yoma and crossed the flooded paddy field area to approach the Sittang river. Every available British tank, gun, mortar and machine gun was at once committed against it and, despite low cloud and heavy rain, every warplane that could be got off the ground was also used. The Thunderbolt could carry three 500-lb (227-kg) bombs and the Spitfire one 500-lb (227-kg) bomb, and operating as complete squadrons these warplanes wrought havoc among concentrations of moving Japanese troops. Many incidents occurred where RAF ground observers exposed themselves to friendly fire, and several were wounded by British bomb fragments as they called down fire very close to their own positions. The British artillery, most of its comprising 5.5-in (140-mm), 4.5-in (114-mm) and 25-pdr pieces, devastated the Japanese in a process that lasted to the end of July.

Toward the end of July this last desperate Japanese offensive had been brought to a halt. The 15th Army then stepped in an effort to help the shattered survivors of the 28th Army. Karen guerrilla forces were able to ambush hundreds of the escaping Japanese and attack elements of the 15th Army. The British Force 136 liaison organisation operated with the Karen units, and used Westland Lysander army co-operation aircraft to evacuate the seriously wounded, prisoners and documents, and in return to bring in urgently needed supplies. The Lysander aircraft also located targets not only for Spitfire and Thunderbolt fighter-bombers, but called on the Bristol Beaufighter heavy fighters and de Havilland Mosquito fighter-bombers of Air Marshal Sir Alec Coryton’s 3rd Tactical Air Force. By 29 July the 15th Army had pulled back after realising that the break-out was a disaster, but had succeeded in rescuing a small number of scattered groups.

By the time the battle died down only a few Japanese units had managed to cross the river, having reached the Sittang by 7 August before the whole area was cleared by British infantry.

The Japanese break-out had been a great failure and further sapped already low Japanese morale. The remnants of the 28th Army were now so small that the task of harrying them was devolved to the Karen guerrillas and the RAF. Even so, Messervy and Stopford each described the break-out as a heroic effort, and stated that most of the 660 men taken prisoner were captured only because they were incapable of further effort, a fact which highlighted, if such were necessary, the tenacity of the Japanese even when starved and totally shattered by disease.

Of the Japanese losses, the unit which suffered the lowest percentage of casualties was Matsui’s 105th Independent Mixed Brigade: of 4,173 men more than 2,000 got across the Sittang river. On the other hand, the 13th Naval Guard Force was annihilated as only a handful of its original 600 men escaped. A number of Japanese (at least 70 and perhaps more) had deserted while still in the Pegu Yoma, and the 28th Army suffered the heaviest casualties of any formation in 'Hai' (iii): the 54th Division had suffered huge proportionate casualties, with more than 5,000 men lost breaking out across the Sittang. Of the 55th Division's 9,000 men who began the break-out, fewer than 4,000 reached Tenasserim. Thus, from the 18,000 men directly controlled by the 28th Army, fewer than 6,000 managed to reach the eastern bank of the Sittang river. The British forces lost 1,500 to disease throughout the period, but suffered a mere 95 men killed and 322 wounded, the latter including a small number to 'friendly fire' accidents.

The Royal Air Force flew 3,045 sorties and dropped some 750 tons of bombs. This and carefully planned and executed artillery fire plans caused the majority of Japanese casualties.

With the defeat of 'Hai' (iii), the Burma Area Army became a military irrelevance in the South-East Asia campaign. With most of Burma now liberated, the news that Japan had surrendered on 15 August only increased the anxiety of the Japanese to get to the Tenasserim hills. They did not wish to be immobilised on the eastern bank of the Sittang river, however, and another 2,000 Japanese died after the Battle of the Sittang Bend had been fought, many of them in the first days after Japan’s surrender.

On 13 September the last remaining units of the once formidable Burma Area Army surrendered to the British.