'Mastiff' was the British successor to 'Birdcage', in which leaflet drops had told Allied prisoners of war in Japanese hands that Japan had surrendered, for the delivery of the first stages of material aid (August/September 1945).

As such, 'Mastiff' was designed to bring physical rather than morale relief to the inmates of the camps, and its first flights were undertaken late in August 1945 to known camps in Burma, Thailand and northern Malaya, and by early September the flights had been extended in range to camps in southern Malaya, Singapore, Thailand, Indo-China, Sumatra and Java. To complement the food and medicine drops of 'Mastiff', special teams were also airdropped into the camps to take over administration, medical aid and food tasks until larger parties could be brought in.

By the end of September about 53,700 prisoners and internees had been evacuated to Australia, India and the UK, the total rising to 71,000 by the end of October. By May 1946 some 96,575 prisoners and internees had been evacuated in a programme analogous to 'Exodus' (ii) in Europe.