'Lethal' was a British unrealised plan, developed from 'Arabian', for the capture of the U-boat bases in the Brittany peninsula of German-occupied France (summer 1943).

Planning was terminated when it was appreciated that the required forces (men and amphibious capability) would be needed for the 'Husky' (i) landings on Sicily, and that a landing operation so far from support (especially air support) from the British mainland would be fraught with operational difficulties and therefore was probably not worth the risk.