'Langtoft' was a British deception by the London Controlling Section to conceal from the Germans the Allied reduction in the manufacture of chemical warfare weapons, to discourage the Germans from resorting to chemical warfare, and yet also dissuade the Germans from curtailing their economically and industrially expensive preparations for defence against attack by chemical warfare weapons (February 1943/May 1945).

Undertaken almost wholly by 'special means' (double agents), 'Langtoft' promulgated the 'story' that the British had new and highly effective types of gas for offensive purposes, and improved gas masks and protective clothing for defensive purposes.