This article explores the pivotal, but largely neglected 1977-1978 German neutron bomb (ERW) controversy in its broader domestic and international contexts. It explains how a domestic ideological intra-Social Democratic Party (SPD) argument over “security” and “Germany” between chancellor Schmidt and SPD executive party secretary Bahr turned a secret governmental issue—the question of ERW production and deployment—into a highly politicised public debate. Internationally the ERW affair revealed a deep Euro-Atlantic rift and rapidly worsening East-West relations which could threaten the “German” situation. On the domestic scene Bahr used the opportunity to stimulate moralist-pacifist thinking within his party and among the wider public by which he not only risked association with Soviet peace diplomacy, but also challenged Schmidt's political authority and strained the government coalition beyond repair. Above all, however, it provided the political context for Schmidt to embrace an international leadership role by verbalising his initial ideas of what in 1979 would become NATO's landmark “dual-track decision.