The function of outpost of the Anglo-Indian empire and base for supplies to China, made Burma take on considerable military importance in the theater of war in the Far East. The Rangoon-Mandalay-Lashio railway (which branches off from Mandalay to Myitkyina) continues towards China on the so-called “Burma road”, completed in December 1938, which reaches Ta-li via Lung-ling. Japan had obtained, on July 18, 1940, a commitment from Great Britain not to allow war material to go through it for three months, destined for Ch’ang Kai-shek, but, in October, the agreement was not renewed and the aviation Japanese tried, but always with poor results, to interrupt the road, bombing the section that crosses the Yün-nan. On January 20, 1942, Japanese troops flowed into southern Burma from Thailand’s western frontiers; on 1 February they seized Moulmein between 1 and 5 February they forced the lower course of the Saluen river into fierce fighting, conquered Martaban and developed a wide-ranging maneuver, to circumvent the left wing of the Anglo-Indians, who retreated behind the Sittang. On 1 March, the Japanese reached Pegu, cutting the Mandalay-Rangoon railway line and the British, threatened with encirclement, cleared the capital, entrusting its defense to rearguard units that fought against overwhelming Japanese forces, to which, on 9 March, they had to give up the city. In the same day, General Sir Harold Alexander assumed command of the allied forces in Burma and entrusted the Sittang sector to the Chinese troops and the Irawady sector to the Anglo-Indians. The Japanese pressed north, reached the port of Bassein on March 19, encircled Taungu on March 26, overcame Prome in April and gained full control of lower Burma. They moved towards the oil region of Yenangyaung where the British carried out – as they officially announced on April 18 – the destruction of all oil extraction plants. On April 30, Japanese troops, coming from the Sittang valley, entered Lashio and walked towards China, on the “road to Burma”, the use of which was thus taken away from the Anglo-Chinese. The invasion of Burma developed in every sector from Saluen to Arakan and, while General Alexander under the protection of Indian “gurkha” units made a painful retreat towards the borders of Bengal and Assam, Japanese troops occupied Maridalay on 1 May, then Myitkyina, on the 8th the port of Akyab, and approached the Indian border; one unit went as far as Chittagong.
The war in Burma suffered a halt until November 1943, interrupted, between the end of 1942 and the beginning of 1943, by an episode that the general AP Wavell had made by Anglo-Indian departments in the direction of Akyab, which was almost reached. But the Japanese quickly counterattacked and, in May, they entered Bengal for a few tens of kilometers.
In August 1943, at the Quebec conference, Admiral Lord Louis Mountbatten was entrusted with the newly established “South-Eastern Asia Command” and the task of reconquering Burma, starting from Assam, with the help of the 1st Chinese army from the China and with the participation of American departments. The offensive was initiated by the 14th and 50th Chinese divisions, under the orders of General JW Stilwell, who had been trained and armed in India with American material and airborne to the area north of Ledo. They, in March 1944, attacked, overcoming the stubborn Japanese resistance, descended into the Hukawng valley; on 20 June they occupied Mogaung and on 3 August also Myitkyina, the terminus of the railway to Mandalay. Meanwhile, the 1st Chinese Army, having crossed the Saluen.
The Japanese then devised a counter-offensive maneuver that would disrupt the opposing line-up, breaking into Manipur in order to threaten the Bengal-Assam railway and to cut off supplies from India to the Sino-American troops engaged in the Ledo-Myitkyina sector. At the same time, they tended to seize the airfields of north-eastern India, used for air transport to China, and to create the possibility of acting behind the Anglo-Indian troops of the Arakan sector. They managed, in the months of March and April 1944, to achieve some success with the encirclement of Imphal, but the reaction of the Allies, which developed in the months of May, June and July, thwarted the threat and forced the Japanese to return to their starting positions.. Lord Mountbatten, which had a group of armies strong of 750,000 men, resumed in September the campaign for the reconquest of Burma, which took place mainly in the four sectors of Arakan, Chindwin, Bhamo and Yün-nan. The fighting was particularly fierce in the Chindwin sector, where the 14th Anglo-Indian army (Gen. W. Slim) had to overcome the fierce Japanese resistance to clear the way on Kalemyio and towards Palel, and in Yünnan, where the Chinese, who they had reached Lungling since September, were counterattacked, forced to give up ground and to keep pace for some time. The obvious purpose of the Japanese command was to delay the Allied march on Rangoon, at least until May 1945, when the monsoons would help stop operations for six months. so as to postpone the total reoccupation of Burma to 1946 and, consequently, the operations for the liberation of Singapore. But the Allies relentlessly pressed and, in November, the Chinese forces of Yün-nan entered into connection with those coming from Myitkyina, thus giving the possibility to establish the connection of Assam with “the road to Burma”.
On November 3, Stilwell left the command of the Sino-American troops, which was assumed by the gen. Wedemeyer. Operations continued unabated. Alternating rapid bids with landings, northern Arakan, with the important port of Akyab, was recaptured by May 1945; the Chinese returned to Lashio on 7 March 1945; the 14th Anglo-Indian army, which had reached the Irawady at the end of January on both sides of Mandalay, overtook it in March, overpowered the 15th and 33rd Japanese armies and headed south, while the 19th Indian division seized of Mandalay. The Japanese tried to slow down, with disturbing actions, the march of the adversaries to Prome on the Irawady, and to Thazi on the Sittang; but the Anglo-Americans resumed the thrust on Rangoon in mid-April, preceded by motorcycle units, refueled by air. Pegu was overtaken on April 29 and Prome on May 3, the same day that Rangoon fell. A campaign followed against the surviving Japanese groups, one between Sittang and Irawady and the other in Arakan. On August 26, 1945, the surrender deed was signed in Rangoon; but the last Japanese troops did not lay down their arms until 13 September.