The British Army evolved from being a large citizen army reliant on conscripts to being a small, all-professional army consisting of volunteers. This was accompanied by its transition from being a force primarily composed of young, unmarried men to one mainly comprising married soldiers. As the Army shrank and the nature and dynamics of Army life evolved, a growing gulf emerged (or re-emerged) between civilian society and Britain’s small professional Army. British society underwent a cultural and religious transformation. In the early 1950s, it was governed by conservative Christian values and norms, and the great majority of Britons identified as Christian. By the early 2020s, this was no longer true, and the salient characteristics of British ‘Christendom’ had largely disappeared. While Britain became an increasingly secular and multi-religious society from the 1960s, the legacy of two world wars and the threat of nuclear Armageddon propelled mainstream Christian opinion towards a position of ‘functional pacifism’. This chapter highlights the implications of these developments for religion in the Army and considers the sources on which a study of this kind can be based.