'Appendix Y' was the Allied interim designation for the cover and deception operation originally designated as 'Torrent' and itself replaced by 'Mespot' and 'Fortitude', to support 'Neptune' (iii) and 'Overlord' (spring/summer 1944).

Created under the auspices of the COSSAC (Chief-of-Staff Supreme Allied Commander) team, the plan was intended to suggest a major amphibious landing by a force of six divisions in the region of the Pas de Calais on the north-east coast of German-occupied France.