South East Asia Command

South East Asia Command (SEAC) was the body set up to be in overall charge of Allied operations in the South-East Asian Theatre during the Second World War.

The initial supreme commander of the theatre was General Sir Archibald Wavell while head of the short-lived American-British-Dutch-Australian Command (ABDACOM) which was dissolved after the fall of Singapore and the Dutch East Indies. On 30 March 1942 the Joint Chiefs of Staff issued instructions naming General Douglas MacArthur as commander-in-chief of the South West Pacific Area, which was made responsible for the water areas of the South China Sea, Borneo, and Java.

In August 1943, the Allies created the combined South East Asian Command, to assume overall command of air, sea and land operations in the theatre. In August 1943, with the agreement of the Combined Chiefs of Staff, Winston Churchill appointed Admiral Lord Louis Mountbatten as Supreme Allied Commander South East Asia. US Army General Joseph Stilwell was appointed deputy supreme commander. Stilwell was also, officially, deputy to Chiang Kai Shek, as Allied commander in China, and commanded all US forces across both theatres (which were known in the US as the China Burma India (CBI) Theater). Meanwhile the British Army commander in India, Auchinleck as Commander-in-Chief, India, provided vital base support.

Mountbatten arrived in India on 7 October and SEAC came formally into being in Delhi at midnight on 15/16 November.

SEAC headquarters moved in April 1944 to Kandy in Ceylon.

From the outset, Western Allied forces available for the wider war against Japan were limited – by an overall Allied commitment towards defeating Nazi Germany, before the Empire of Japan. This was especially the case for the UK, and major advances were not anticipated in Asia until mid-late 1944 at least – that is, not until the defeat of Germany had become inevitable.

A strategic focus by the Western Allies on the Central Pacific (i.e. the "Pacific Ocean Areas" in contemporaneous Allied terminology) and the South-West Pacific, resulted from compromises reached at the Casablanca Conference. UK participants were focused on Nazi Germany, and saw the war against Japan being limited "to the defense of a fixed line in front of those positions that must be held". However, because such an approach was unacceptable to the United States, it was agreed that there would be offensive actions in Burma, operations in support of China, and other activity beyond holding a defensive line in South East Asia, as a result of US demands that the Japanese be kept off-balance, throughout any areas in which they might encounter Allied forces. Nevertheless, for the Western Allies, the South East Asia theatre, China, and the North Pacific (including Alaska), were destined to become secondary theatres, relative to efforts in the Pacific Ocean Areas, in which the supreme commander was US Admiral Chester Nimitz. Some saw SEAC as an organization for recapturing colonial possessions. The British also sometimes appeared to be more interested in liberating their own Asian possessions than the Americans did. This led Washington to try to distance itself from SEAC politically.

On 2 December 1943, the Combined Chiefs of Staff officially approved in principle a plan designating the Pacific Ocean Areas as the focus of the main effort against Japan. Their reasoning was that advances in the Central Pacific were the most rapid route towards sustained, direct attacks on the Japanese Home Islands – e.g. subjecting Tokyo and other major cities to attacks by strategic bombers. A secondary line of advance – by US and Australian forces – "along the New Guinea-N.E.I.-Philippine axis", was to be controlled by the separate South West Pacific Area command under Douglas MacArthur (US Army).