The war cabinet had already commissioned a report called "British Strategy in a Certain Eventuality", drafted by the Chiefs of Staff (CoS). The report concluded that resistance to the Wehrmacht would be impossible if they gained a secure foothold in Britain: without the bulk of the army stranded in France, the home-based forces and civil defence would be inadequate. The CoS held that air defence was crucial and that the United Kingdom could not survive if Germany gained control of the air, although the Royal Navy would at least provide some breathing space. It had been calculated that Germany's air superiority was about four to one and it was vital that the British war effort must concentrate primarily on the production of fighter aircraft and crews, and the defence of those factories essential to fighter production should have priority.