'Flabbergast' was a British deception operation designed by the 'D' Division to support the 'Extended Capital' and 'Dracula' (ii) recapture of central Burma and Rangoon by Lieutenant General Sir William Slim’s 14^th Army by suggesting to the Japanese that the higher-priority British intention was the recapture of Malaya via Sumatra in the Netherlands East Indies (September/October 1944).

'Flabbergast' had only a one-month life, and on 21 November the definitive deception for 'Extended Capital' became 'Stultify'.