This is a study of a successful parliamentary campaign led throughout the 1920s by a small group of backbench Labour MPs aimed at abolishing the military death penalty for the offences of cowardice and desertion. It was sustained in the face of opposition from the military establishment, the Conservatives, and finally the House of Lords. The campaigners used the opportunity afforded by the requirement on government to pass, annually, an Army Bill, to challenge the military establishment's insistence that a capital penalty was essential to the maintenance of army discipline. Despite the unwillingness of the 1924 Labour government to confront the military on this issue, the reformers persevered, securing some minor, incremental reform before the coming of the second Labour government in 1929. The new government was prevailed upon by backbench pressure to authorize a free vote in the Commons which approved the abolition of the capital penalty for cowardice and desertion in the Army Act of 1930.