Quote:
Until 1941, the defense of Burma ranked below that of the West Indies in the list of British priorities. Burma possessed little strategic importance and relatively few natural resources apart from rice. The Japanese occupation of southern Indo-China in July 1941, however, presented Burma with a real external threat, but the higher claim of Malaya and Singapore on military resources meant that in December 1941 the military establishment in Burma consisted of a few combat aircraft and the equivalent of one division.
For Japan, Burma’s occupation would sever the Chinese Nationalist’s main line of communication with the outside world (via Lashio and Rangoon) and would provide defense in depth to the southern resources area. The Japanese high command thus ear-marked the 15th Army for operations in Burma after the occupation of Siam was complete.
The 15th Army, with just one regiment under command, occupied the Kra Isthmus between Prachaub and Nakhorn on 8 December, to secure the rear and the lines of communication of the 25th Army as it advanced into Malaya. Victoria Point airfield was secured on 16 December, but it was not until then that the 15th Army began operations in earnest. Airfields at Tavoy and Mergui were secured and from them Japanese fighters were able to escort bomber raids on southern Burma for the first time. By the end of January the port of Rangoon had been brought to a standstill.
The main Japanese effort was made, however, on the Raheng-Moulmein track. The 15th Army had two half-strength divisions under command when it crossed the border on 20 January, but these possessed superiority of numbers over a defense divided between Tenasserim and the Shan States, and which was committed to defending Burma east of the Salween. Despite the arrival at Rangoon of four brigades in the six weeks before the city’s fall, the destruction of the 17th Indian Division doomed the capital, and with it any British hope of holding Burma.
It had been the original Japanese intention to secure Rangoon and then advance into central Burma and with the end of the other campaigns in southeast Asia the Japanese were able to move the equivalent of three divisions by sea to Burma within seven weeks of the capture of Rangoon. The 15th Army quickly developed its offensives in the Irrawaddy Siitang valleys, despite the presence there of Chinese forces (which were dispersed, equivalent to no more than a division and, on the Siitang, were not mutually supporting). The first crucial clash around Toungoo was won by the Japanese. Critically, the Japanese secured the bridge over the Siitang intact and were able to develop an offensive through the mountains which resulted in the capture of Lashio on 28 April. Four days later the Japanese secured Mandalay and with it control of central and northern Burma.
The formal decision to abandon Burma was not taken until 25 April, by which time the withdrawal was threatened as much by the approach of the monsoon as the advancing Japanese. In the first week of May the last British formations in Burma, plus one Chinese division, abandoned the lower Chindwin and began the trek to Imphal, whilst the remainder of the 5th Chinese Army withdrew into northern Burma and thence to either Assam or northern Yunnan. Parts of the 6th Chinese Army contrived to remain in the eastern Shan States, but on the 66th Army’s front the Japanese advanced into Yunnan and established themselves on the Salween, where they were to remain until late 1944.
The Japanese presence in most of Burma preoccupied British strategy in the East until 1944. Supplies to Nationalist forces in China were disrupted, but the incipient threat to India was never realized, although an assault on Ceylon and other ports signposted disruption of shipping in the Indian Ocean and caused fears of Japanese designs on Madagascar.
The most complete site I've ever found on the CBI: