'Dummer' was a British cover plan for 'Lifebelt', the planned seizure of the Azores islands group in the spring of 1943 initially planned as 'Brisk', and then for 'Alacrity', the actual agreed occupation of October 1943 (spring/October 1943).

The cover plan was based on information leaked to the troops involved that they were bound for the Mediterranean theatre and an invasion of the Axis-occupied French island of Corsica.