'Masterdom' was the Allied plan for the occupation of Indo-China after the Japanese surrender, planned in parallel with 'Bibber' for Thailand (1945).

Drafted by Admiral the Lord Louis Mountbatten’s South-East Asia Command, 'Masterdom' called for the 'Maelstrom' movement, by air to Saigon via Bangkok, of Brigadier D. E. Taunton’s Indian 80^th Brigade of Major General D. D. Gracey’s Indian 20^th Division, elements of the RAF’s Nos 28 and 684 Squadrons, and an Allied control commission. This initial step was to be followed by the delivery of the rest of the Indian 20^th Division by sea. The total requirement was to move 25,750 men and 2,400 vehicles to Saigon, where Gracey was to exercise full control of the region until the French could re-establish themselves, issuing orders directly to Field Marshal Count Hisaichi Terauchi, commander-in-chief of the surrendered Southern Expeditionary Army Group.

The British imagined that there were some 71,000 Japanese troops in Indo-China, though the reality was something like 2,000 in the headquarters of the Southern Expeditionary Army Group and of Lieutenant General Yuitsu Tsuchiashi’s 38^th Army, 8,000 in Lieutenant General Takanobu Manaki’s 2^nd Division, 1,000 in Lieutenant General Ryozo Sakuma’s 55^th Division, 7,700 in miscellaneous army units, about 9,000 air personnel at 35 air bases, and about 2,500 naval personnel. About 28,500 men were on the strengths of the forward headquarters of the 38^th Army, Lieutenant General Naotomi Mikuni’s 21^st Division and Lieutenant General Masachika Hirata’s 22^nd Divisions, and the 34^th Independent Mixed Brigade, all located in northern Indo-China or Thailand and thus the responsibility of the Chinese or occupation forces in Thailand.

'Masterdom' began on 8 September, but logistical difficulties meant that the Indian 80^th Brigade and one squadron of Supermarine Spitfire fighters were not fully assembled until 26 September, by which time Gracey was fully embroiled in the politics of the region, where the Emperor of Annam had abdicated in favour of the Republic of Vietnam and in which large areas were controlled by the Viet Minh communist guerrillas. Gracey’s two other units, Brigadier E. C. J. Woodford’s Indian 32^nd Brigade and Brigadier C. H. B. Rodham’s Indian 100^th Brigade, arrived shortly after this, allowing the British commander to use larger numbers of Japanese troops and thus take a firmer stance with the local dissidents as the troops of Général d’Armée Philippe François Marie Jacques Leclerc de Hauteclocque’s French administration began to arrive (5ème Régiment d’Infanterie Coloniale and a combat command of the 2ème Division Blindée), with more units (9ème Division d’Infanterie Coloniale from France and the Brigade d’Extrême-Orient from Madagascar) in transit or about to be despatched, and the 3ème Division d’Infanterie Coloniale promised for a later date.

Small-scale actions kept the Viet Minh under control, and the French began to assume control on 19 December, allowing the British to complete their evacuation of Indo-China by 13 May 1946, when full responsibility was given to Contre-amiral Georges Thierry d’Argenlieu, the French high commissioner.