Using previously unresearched archives from the British Council of Churches (BCC), a constituent assembly of the World Council of Churches and the established vehicle for communicating official non-Catholic approaches of the nuclear dilemma, this thesis raises two questions: (1) How did Christians in the BCC evaluate the role of the British State and their responsibility as citizens in the Cold War years 1945-59? (2) How did such evaluations affect a Christian policy-making process that aimed to influence Western defence attitudes? Answers are provided by analysing the BCC's role in developing and promoting the limited war nuclear strategy, a just war alternative to the Macmillan Government's formula of massive retaliation. The study contends that the British Churches' stance vis-à-vis the ethics of nuclear deterrence was largely influenced by judgements on the legitimacy of the State and its compatibility with Christian values. These judgements determined the nature of advice offered to Government and favoured the articulation of an 'Augustinian' form of political realism. The thesis makes two substantive claims. On one hand it suggests that the significance of the BCC approach lay, not in its challenge to Government policy, but in its role as a counter to the radical idealism represented by the Campaign for Nuclear Disarmament. On the other hand it argues that the just war should be conceptually located within the realist rather than idealist theoretical frameworks. The study concludes that discussions of just war cannot be separated from qualitative judgements about the character of the State. Christian attitudes to war are grounded in particular assumptions about legitimate social authority, the right of the State to determine policy, personal and collective political responsibility.