The 'Yunnan-Borma Road Operation' was part of the Chinese intervention to aid their British allies as the Japanese attempted to consolidate their 'B' (iii) invasion of Burma (mid-March/early June 1942).

The Chinese forces involved in this undertaking were Lieutenant General Tu Yu-ming’s 5^th Army (three brigade-sized divisions), Lieutenant General Kan Li-chu’s 6^th Army (three brigade-sized divisions) and Lieutenant General Chang Chen’s 66^th Army (three brigade-sized divisions) under the overall command of the Chinese Expeditionary Force in Burma led by Lieutenant General Joseph W. Stilwell with Lieutenant General Lo Cho-ying as his chief-of-staff and commander of the 1^st Route Expeditionary Forces.

In February 1942, Lo ordered the 5^th Army to move from western Yunnan to the vicinity of Toungoo in northern Burma and thence to advance farther to the south in the same British colony. Under the command of the divisional commander, Major General Tai An-lan, advanced elements of the 5^th Army’s 200^th Division reached Toungoo on 8 March and took over the town’s defensive positions from the local British forces. The 6^th Army was directed to move from Kunming to the Burma/Thailand border, and its leading elements reached Mawchi, Mong Pan and Mong Ton in the middle of March. The 66^th Army later arrived in Lashio and Mandalay as a reserve and to assist the British forces.

The battles of the Yunnan-Burma Road campaign were the Battle of Tachiao (18/19 March), the Battle of Oktwin (20/23 March) in the vicinity of Oktwin, the Battle of Toungoo 24/30 March) in and around Taungoo, the Battle of Yedashe (5/8 April) in the vicinity of Yedashe, the Battle of Szuwa River (10/16 April) on the Szuwa river to the north-west of Yedashe, the Battle of Mawchi and Bato (early April) in the vicinity of Mawchi, the Battle of Bawlake (17 April) in the vicinity of Bawlakhe, the Battle of Yenangyaung (17/19 April). the Battle of Pyinmana (17/20 April) in the vicinity of Pyinmana, the Battle of Loikaw (20 April) in the vicinity of Loikaw, the Battle of Hopong-Taunggyi (20/24 April) in the vicinity of Hopong and Taunggyi, the Battle of Loilem (25 April) in the vicinity of Loilem, the Battle of Lashio (29 April) in the vicinity of Lashio, the Battle of Hsenwe (1 May), the Battle of the Salween River (6/31 May), and the Battle of the Hsipaw-Mogok Highway (23 May).

The Battle of Tachiao was thus the first clash in the 'Yunnan-Burma Road' campaign, and began on 8 March as advanced elements of the 200^th Division arrived at Toungoo and took over the defensive positions from the British force currently holding them. Toungoo itself was to be the main defensive position of the Chinese forces, with an outpost a short distance farther to the south at at Oktwin. Tai, the divisional commander, sent his Motorised Cavalry Regiment and 1^st Company of the 598^th Infantry Regiment to the banks of the Kan river about 37 miles (60 km) to the south of Toungoo and 12.5 miles (20 km) to the south of Pyu. The cavalry regiment and one company of infantry pushed up to Kan river, with a platoon of cyclists taking up positions at the bridge over the river.

At first light on 18 March, about 200 Japanese reconnaissance troops of the 143^rd Regiment of Lieutenant General Hiroshi Takeuchi’s 55^th Division, itself part of Lieutenant General Shojiro Iida’s 15^th Army, advanced right up to the bridge on motorcycles but, on reaching the outposts were ambushed by the Chinese troops hiding along the sides of the road. Chinese armoured cars joined the attack and after three hours of fighting the Japanese fell back, leaving about 30 dead together with some weapons and equipment. After the fall of night, the Japanese resumed the attack with small units, and the Chinese covering force fell back toward the defence line at Oktwin. Following on the next day, the Japanese took Pyu on 19 March.

The Battle of Oktwin started on 20 March as the Japanese 143^rd Regiment plus cavalry units of the 55^th Division attacked the positions of the Chinese 5^th Army Cavalry Regiment in the area to the north of the Kan River, driving the Chinese back with heavy losses. Most of the cavalry regiment was withdrawn to the north of Toungoo, leaving only single companies of infantry and cavalry to delay the advancing Japanese. Meanwhile, the field fortifications ordered by Tai at Oktwin and around Toungoo were now ready. These defences were constructed from the locally abundant timber, and were carefully sited and concealed. On 21 March, Japanese forces brushed aside the delaying forces and reached the 200^th Division’s outposts at Oktwin.

The 122^nd Regiment of the 55^th Division attacked 200^th Division’s positions at dawn on 22 March but made little progress. The Japanese forces at this time comprised one battalion of infantry with several pieces of artillery, while the defence was based on the 1/600^th Regiment. The Japanese sent cavalry elements round the left flank of the Chinese, and the Oktwin position was stabilised only when reserve forces of the 1/598^th Regiment immediately counterattacked.

After having being ambushed, the Japanese were now more careful, and used artillery and machine guns to fire at suspected positions before sending forward their infantry. They also positioned light machine guns among the trees, and these caused many Chinese casualties. Eventually the Chinese positioned heavy machine guns to deal with this threat.

On 23 March, the Japanese attacked again on the left flank with strong artillery and air support. The battle continued until 16.00 without much success for the attackers, who then tried another flanking move with a company of infantry and scores of cavalry around the Chinese positions' right flank. The Chinese held their ground until the fall of night and then withdrew to their main defensive line at Toungoo on 24 March.

On 8 March, the date on which Rangoon fell, advanced elements of the 200^th Division reached Toungoo and the division assumed control of the defence of this key location from a small detachment of British forces. Toungoo controlled the road north toward Mandalay and the bridge over the Sittang River that carried the road east to the Karenni States and north to Loikaw, the Shan States, Lashio and the Chinese province of Yunnan. Capture of the town could threaten the flank of the Allied defensive line in Burma and open the way to a Japanese advance into Central Burma.

As noted above, Tai had decided that Toungoo was to be the main defensive position of the Chinese forces, with an outpost line to the south at Oktwin. He sent the Motorised Cavalry Regiment and the 1^st Company of the 598^th Infantry Regiment to the banks of the Kan river. The cavalry regiment and the infantry company pushed up to the Kan river, with a platoon of cyclists taking up position near the bridge at the village of Nyaungchidauk. Here the Chinese were to delay the advance of the Japanese until the defences at Toungoo had been completed.

Meanwhile, the 200^th Division began to entrench itself within the old town walls and at the advanced line at Oktwin. Toungoo itself was divided into the new town lying to the east of the railway line and the old town to the west. 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 from the locally abundant timber. To make things more difficult for the attackers, the land around Toungoo was flat and featureless everywhere except for the Sittang river to the east.

It was some 10 days later, on 18 March, that there started the first skirmish with the leading elements of the 55^th Division on the Kan river at Nyaungchidauk. Falling back on Toungoo during the course of 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 checked for two days by determined Chinese resistance.

On 24 March, the 112^th Regiment delivered frontal attacks on the Chinese positions at Oktwin. The 143^rd Regiment, with the aid of friendly local Burmese, used the cover of the jungle and wooded area to the west of the city in order to make an advance of 3.75 miles (6 km) to the north and attack the airfield and nearby railway station at Toungoo. The area was defended by only one engineer battalion, whose commander withdrew his men in a panic. This cut the 200^th Division’s line of communications to the north, and left it encircled on three sides.

Tai ordered the abandonment of the outlying positions so that he could concentrate his defence near the walls of Toungoo. The 598^th Regiment held the northern part of the defences, the 599^th Regiment the south of the city, and the 600^th Regiment the west. The divisional headquarters was shifted from the town to the eastern bank of the Sittang river in an effort to avoid Japanese air and artillery attacks, and also to safeguard the remaining supply route to the east. Part of a replacement regiment, which had arrived only on the previous day, was positioned on the east bank of the Sittang river to extend the defences to cover the supply line and the divisional headquarters.

At 08.00 on 24 March, the Japanese launched an all-out attack on all three sides of Toungoo with the 143^rd Regiment on the left, the 112^th Regiment on the right and the 55^th Cavalry Regiment plus an infantry company along the Sittang river. The Japanese objective was to drive the Chinese forces against the Sittang river, where they would then be destroyed. Despite local penetrations in the north-western part of their perimeter, heavy Chinese resistance prevented the Japanese making any significant progress until 22.00 when limited numbers of Japanese troops infiltrated the Chinese positions in the north-western part of Toungoo’s citadel, and these were soon followed by a full battalion.

The Chinese reinforced the 600^th Regiment with the 2/598^th Regiment and counterattacked. There was heavy house-to-house fighting, and the gap between the forces was so small that Japanese air and artillery support found it difficult to avoid hitting their own men. The counterattack failed to recover the lost positions, however, when Japanese troops made effective use of the buildings and the stone walls around a local cemetery. The 600^th Regiment was then pulled back between the 200^th Division’s other two regiments to defend Toungoo itself. Elsewhere the bridge over Sittang river became the target for Japanese firepower, and was so severely damaged that vehicles could not cross it.

The Japanese attack continued on 26 March. The 112^th Regiment took the south-western corner of Toungoo, but was unable to make further progress. On the left, a flanking move to fall on the north-western part of Toungoo was no more successful. The 55^th Cavalry Regiment's attack was also repulsed. The Chinese launched a 300-man counterattack in each of the three sectors against the 112^th Regiment and the 55^th Cavalry Regiment, but these were repulsed with losses so heavy that the Chinese offensive strength dropped markedly.

By the evening, the Japanese had taken the western part of the city to the west of the railway line, while the Chinese troops maintained their hold on the main part of the city to the east of the railway line. The two sides faced each other across the railway line at a distance of less than 110 yards (100 m), making it difficult for Japanese to provide their forces with air and artillery support. For this reason, the Japanese eventually withdrew some 220 yards (200 m) to allow their planes and guns to operate. During the resulting bombardment, the Chinese hid in their camouflaged positions then held their fire until the Japanese advanced, and only when the Japanese were within 45 and 55 yards (40 and 50 m) did they open fire with machine guns and grenades. This happened several times, and by the end of the day the 200^th Division had taken very heavy casualties; the the Japanese had also suffered heavily and were finding it hard to continue the frontal attacks. The arrival of the New 22^nd Division to the north of Yedashe forced the Japanese to send the 2/143^rd Regiment to Nangyuen as a blocking force to stop the Chinese reinforcement from reaching Toungoo, and this greatly reduced Japanese attacking strength at Toungoo itself. The 144^th Regiment, the third of the 55^th Division's regiments, as well as a battalion of artillery and a company of cavalry were not with the division in the Battle of Toungoo, so the division lacked sufficient manpower and as a consequence the Japanese attack stalled.

During the morning of 27 March, there was a pause in the fighting, but Japanese warplanes returned in the afternoon and systematically bombed and strafed the Chinese positions. With this renewed air support, the Japanese were able to press their attacks, and in the afternoon they also fired large numbers of tear gas shells. Despite all this, the Chinese held their ground, and the Japanese now decided to await the arrival of the 3^rd Heavy Field Artillery Regiment, equipped with 5.91-in (150-mm) howitzers, before resuming their attack on the Chinese positions on 28 March, when air support was also provided.

On March 28, with the 3^rd Heavy Field Artillery Regiment and strong air support available, the Japanese inflicted heavy casualties on the Chinese. The right wing of the attack destroyed many Chinese strongpoints, but the light bombers of the promised air support did not arrive until 15.00 as there had earlier been heavy fog at the airfields. This the Japanese could not overcome the stubborn resistance of the Chinese, who had defences in depth. The fighting lasted into the evening.

Meanwhile, the 56^th Reconnaissance Regiment of Lieutenant General Yuzo Matsuyama[s 56^th Division, comprising two motorised infantry companies, one machine gun company, one field artillery company with mountain guns and one platoon of engineers, was moving rapidly to the north from Rangoon in a convoy of 45 trucks, with a company of six armoured cars and a total of some 404 men. This force made rapid progress along the main road to Toungoo and reached the 55^th Division's headquarters by 12.00 on 28 March. It was decided to move this force to the eastern side of the Sittang river for an attack on the rear of the Chinese positions. At 20.00 the same day and leaving its vehicles, the reconnaissance regiment forded the Sittang river at Wagyi, a short distance to the south of the town at a point where the water was only chest high.

If the Japanese attack to the east of the Sittang was successful, the entire 200^th Division would be encircled. Tai personally supervised the organisation of the defence, and two companies of the 3/598^th Regiment were ordered to attack the exposed left flank of the Japanese. A vicious fight continued within Toungoo itself and, around the divisional headquarters on the river’s eastern bank, the fighting inflicted further heavy losses on the 3/599^th Regiment as well as the divisional support company. Even so, the Chinese were able to hold their ground.

On 29 March, the 55^th Division committed its last strength to attack once more with the support of all available artillery. By 12.00, the Japanese troops on the left were able to advance into the north-western part of Toungoo, and the Chinese line of communications was threatened. Covered by the fighting to the west, the 56^th Reconnaissance Regiment moved to the north and attacked the Chinese flank guard to the east of the river, and by 12.00 had overrun it, thereby threatening the divisional headquarters and the Sittang river bridge.

During the afternoon of the same day, there arrived orders for the withdrawal in the same evening of what was left of the 200^th Division, which was head first to the east and then to the north along the eastern bank of the Sittang river. Fighting within Toungoo continued into the dark hours, by which time the town was ablaze. The Chinese maintained their stubborn resistance, however, and the Japanese initially made no progress. By 22.00 the 56^th Reconnaissance Regiment had closed on the bridge over the Sittang river and as night fell could signal that it had detected signs of wavering in the Chinese ranks.

This was not, however, any failure of determination but rather the start of the Chinese withdrawal. Tai ordered each of his battalions to leave a rearguard, and these night attacks to cover the withdrawal of the main force. The retreat was led by the 599^th Regiment and then the 600^th Regiment, which crossed the battered and threatened bridge, and the 598^th Regiment, which forded the river. By 04.00 the 200^th Division had left Toungoo in good condition, taking all its wounded. The Chinese claimed that their rearguards left before the arrival dawn on 30 March.

On that morning, the 55^th Division attacked all along the front, claiming to have met heavy resistance despite withdrawal of most (if not all) of the Chinese. After Japanese engineers had managed to blow the Chinese positions and strongpoints at 08.50, the 55^th Division's men finally broke through and linked with elements of the 56^th Division which had seized the vital Sittang bridge 07.00 and then attacked Toungoo from the east. This ended the battle, leaving the Japanese in possession of the town and bridge: the road to the east was open for the Japanese to attempt the outflanking of the Allied line in Burma.

The New 22^nd Division, which had been despatched to the south to support the 200^th Division, had meanwhile advanced as far as Nangyun railway station, and partially dislodged the 2/143^rd Regiment from their position round the station. The Chinese division also despatched patrols farther to the south toward Toungoo, thereby threatening the Japanese flank and rear. The surviving parts of the 200^th Division met the New 22^nd Division’s patrols at Yedashe after withdrawing to the north along the Sittang river’s eastern bank to the east of Nangyun. The Chinese next withdrew to new defensive positions at Yedashe, where they planned continue blocking of the Japanese as the latter advanced up the Sittang river valley.

There followed a number of other battles as the Japanese advanced toward China before the next major engagement took place as the Battle of Yenangyaung.

After the Japanese had taken Rangoon, the Allies had regrouped in central Burma. The newly formed Burma Corps, commanded by Lieutenant General W. J. Slim and comprising British, Indian and locally raised Burmese troops, attempted to defend the Irrawaddy river valley, while the Chinese Expeditionary Force in Burma defended the Sittaung river valley to the east of the Irrawaddy river. After they had completed their seizure of Singapore and the Dutch East Indies, the Japanese were now in the position to use divisions released by these successes, together with captured trucks, to reinforce their forces in Burma and launch attacks into central Burma.

One of the Japanese objectives in the Irrawaddy river valley was the complex of oil fields and refineries in the area round Yenangyaung, and the resulting Battle of Yenangyaung began on 10 April. The Japanese attacked Major General J. B. Scott’s 1^st Burma Division on the Allied right and the Indian 48^th Brigade at Kokkogwa at night in a storm, and were driven back with heavy casualties. On the following day, the 2^nd Royal Tank Regiment was in action near Magwe at Thadodan and Alebo. From 13 to 17 April, the British fell back under the weight of the Japanese attacks. On several occasions Japanese roadblocks split the Burma Frontier Force (an internal security force serving as infantry), the 1^st Burma Division, the headquarters of Brigadier J. Anstice’s British 7^th Armoured Brigade and the 2^nd RTR into three.

On 15 April, Slim ordered the destruction of the oil fields and refinery, and the situation was now deemed so critical that General Sir Harold Alexander, commanding the Burma Army, requested Stilwell, the US commander of the China-Burma-India Theater and chief-of-staff to Generalissimo Chiang Kai-shek, immediately to move Major General Sun Li-jen’s Chinese 38^th Division of Chung’s 66^th Army into the Yenangyaung area.

On 16 April, almost 7,000 British troops, together with 500 prisoners and civilians, were encircled by an equal number of Japanese soldiers of Lieutenant General Shozo Sakurai’s 33^rd Division at Yenangyaung and its oil complex. The 33^rd Division had cut the Magwe road between Slim’s two divisions, which were now about 50 miles (80 km) distant from each other. The 1^st Burma Division was hampered by large numbers of wounded men and was short of water, and Scott contacted Sun by telephone to ask for rescue from the encirclement as soon as possible after his 38^th Division had entered the Yenangyaung area.

Sun asked for the authority to take his whole division to the rescue of the 1^st Burma Division, Lo refused his permission. On 17 April, therefore, Sun led his 113^th Regiment of only 1,121 men, of whom a mere 800 were combat personnel, in the rescue mission. Because the Chinese lacked artillery and armour, Slim assigned the 7^th Armoured Brigade to Sun’s command. This British brigade consisted of two battalions of M3 Stuart light tanks and a battery of 25-pdr gun/howitzers.

For the next three days the Chinese attacked to the south in temperatures as high as 114° F (46° C) and under a pall of smoke from the demolished oil wells and refineries.

Meanwhile the 1^st Burma Division fought its way to and across the Pin Chaung river, where it met with the relief column on 19 April. On the next day, the Chinese force attacked to the south toward Yenangyaung and the Pin Chaung. The attack inflicted heavy losses on the Japanese, but the Allied forces were too weak to hold the oil fields and had to retreat to the north.

The 1^st Burma Division had lost most of its heavy equipment and was exhausted and disorganised. Moreover, many of its Burmese troops had deserted.