This article considers how the imagination and expectation of future air raids impacted upon the perception of the built environment, and asks how the boundaries between peace and war, and thus military and civilian, began to be dissolved in this context. It examines the interactions between architects, planners and government officials about how the design of cities and buildings might change in an age of air power. By looking at changes and continuities either side of the 1938 Munich crisis, it examines how the civilian space of cities was recast in anticipation of war.