In 1534, King Tabinschwehti of the small landlocked Toungoo Kingdom in the Sittang valley conquered his father’s former liege’s liege, the much larger but disunited neighbor to the west, the Hanthawaddy Kingdom. The Hanthawaddy ruled over the lands of the mighty Irrawaddy and Chindwin river basins. The Sittang is a mere stream in comparison but both river valleys dominate each other where they spill into the plains of Central Burma: whoever is strongest in one, inevitably will control both. The Toungoo Empire was Southeast Asia’s largest empire and lasted for 300 years.
Four hundred years later in March 1942, the two river valleys were again in an imminent symbiotic relationship where control of one meant control of both. In the Irrawaddy river valley, the newly minted Burma Corps, consisting of the remains of the 17th Indian Division, the 1st Burma Division, and the 7th Armoured Brigade, attempted to reorganize and rally around its newly promoted commander, LieutGen William Slim, who had just arrived from duty in East Africa and Iraq. Slim attempted to concentrate and rally the Burma Corps at Prome on the Irrawaddy after its narrow escape from Rangoon. The Japanese, who usually only operated with nine or ten days of supply (something Slim learned from a Chinese general, and would make use of over the next few years), had out run their logistics. This provided Slim with an opportunity to regroup, but he had several severe difficulties: Morale in the rear areas was collapsing and the civil government was disintegrating. The combat units were understrength and without hope of replacements. He had no direct line supply to India, while the Japanese were already making good use of the port at Rangoon. All of his units were roadbound, and in any case, lacked any jungle warfare training. The tanks of the 7th Armoured were in desperate need of maintenance. And with the destruction of the RAF on the ground in early March (after the short sighted removal of radar and radio detection equipment back to India), he had no air reconnaissance or intelligence network to speak of. He mitigated this last problem by organizing British and Burmese businessmen into an effective, if static screen line between Prome and Toungoo. Furthermore, the Burma Corps was spread out and its subordinate units, specifically the 1st Burma Division away to the east, were not mutually supporting. The 1st Burma was holding Toungoo until it was relieved by Chinese divisions making their way from Lasio and Yunnan. The relief would take almost the entire month of March.
Chiang Kai Shek knew the Burma Road was his lifeline, and in January sent the Chinese 6th Army (equivalent to an understrength Western corps) to reinforce the British in Burma. They would be part of a larger Expeditionary Force of three Chinese Armies, but the rugged terrain and single road prevented the deployment of the force in mass. That the Chinese even arrived at all in Burma was due to the newly appointed commander of the Chinese in Burma, the American LTG Joseph “Vinegar Joe” Stillwell (and to get the lead elements where they were needed most, at Toungoo, Slim used a humorous method by which he had his logisticians place supply dumps farther and farther south on the Mandalay-Tougoo road. The Chinese followed like mice on a trail of cheese until they were finally in position). The irascible and Anglophobe Stillwell was nominally placed under British command, but he was also Chiang’s Chief of Staff, and routinely used his position to circumvent British orders he didn’t agree with. The unity of command was further diluted by the Chinese’s own Byzantine command structure which featured two other Chinese generals who were peers of Stillwell’s: the commander of the Chinese Expeditionary Force in Burma and the Commander of the Chinese Mission to Burma. So the lone unit that finally arrived in Toungoo, the Chinese 200th Division, had five immediate commanders that they were officially subordinate to: one Brit, one American, and three Chinese, and one that they should have been subordinate to, Slim and the Burma Corps, at least until the rest of the Sixth Army arrived across the mountains and from the north. Nonetheless, the 200th Division was one of the toughest, best equipped, best led, and best trained divisions in the Chinese Nationalist Army. They took over the defense of the Sittang Valley at Toungoo while the 1st Burma slowly made their way to their assembly areas north of Prome.
Slim couldn’t wait for them to concentrate, and needed a victory, even a small one to restore some morale to the Burma Corps. The Japanese managed to resupply quicker than expected, and were reinforced by two divisions released from the successful operations in Malaya and the Dutch East Indies. Slim ordered the 17th Indian to attack south of Prome. The attacks were mildly successful, especially against hastily formed units of the Burmese Independence Army under Japanese officers. But traitorous Burmese ambushed isolated British units, and the reinforced Japanese launched their own attack despite the limited British counterattacks. The familiar cycle of Japanese roadblock-British counterattack-British withdrawal, which characterized much of the campaign, initiated. The British finally broke back through at the Battle of Shwedaung but in the process of the withdrawal several units were overrun and massacred. The British again saw to the defense of Prome.
As the British were fighting their way back to Prome, the reinforced Japanese attacked Toungoo. They were in for a rude surprise. The Chinese 200th Division were the only soldiers in Burma that had defeated the Japanese before, and with a week’s preparation were determined to do so again. When the Japanese attacked Toungoo on 20 March, they ran straight into deliberately prepared and well camouflaged defensive positions and were massacred. However, Chinese divisions were understrength compared to their western and Japanese counterparts (only about 9000 troops, of which 3000 are porters) and the weight of numbers began to tell. The convoluted command structure prevented any further Chinese from reaching Toungoo in time. Still, the Chinese fell back to prepared positions inside the ancient walls of the Toungoo Dynasty and made a good fight of it. It looked as if they could hold, at least until Burmese guides brought columns of Japanese through the dense mountainous jungle around the city. The Chinese were forced to withdraw.
The fall of Toungoo to a superior force made Prome and the lower Irrawaddy Valley untenable, as the Hanthawaddy belatedly found out 400 years before. Slim and the Burma Corps retreated further north up the valley where hopefully they could form another defensive line around Mandalay with the Chinese coming over the mountains from Yunnan. But Burma widens significantly after the Prome-Toungoo bottleneck (such as it is) and the successful prospects for such a feat were drastically diminished.