This research focuses on the role of defence in Britain’s European integration during the Cold War. Indeed, Britain’s decision to join the EEC was directly impacted by her military decline. Her financial difficulties resulted in the withdrawal of troops overseas and the demilitarisation of her economy. Her reduced military presence abroad provoked diplomatic tensions with the US, while European security was threatened by the USSR. Furthermore, any war waged between the two superpowers meant the annihilation of Europe. The situation was believed critical, and motivated her entry into the EEC. Britain’s contribution to European defence was undeniable, although perhaps undervalued, and it was a card she played in the conduct of her European diplomacy. In return, her defence policy became increasingly European by the end of the Cold War. Her defence industries had been collaborating significantly in European procurement projects, and she recognised the need for Europe to stand as one in order to be an equal to the US. The case studies show that in time of war, Europe could not rely on the US for support, which led to the formation of a strong sentiment of European solidarity. Nevertheless, it is equally true that European defence integration was constrained by many different political considerations. Most prominently, disagreements over federalisation and its consequences on EEC members’ military sovereignty prevented further defence integration. As a result, the period concluded on the EU founding act, the Treaty of Maastricht, simply leaving the possibility of a European defence community to future leaders, while redefining Europe’s defence policy.