The United States Army Air Corps considered powerfully armed destroyers, like the Bell YFM-1 Airacuda prototype, to counter a potential attack of high-performance bombers. The Lockheed P-38 Lightning and Bell P-39 Airacobra were also initially specified to carry very heavy armament based on a central 37 mm cannon, specified as interceptor aircraft working in the anti-bomber role. Great Britain, by contrast, favored specialized "turret fighters", such as the Boulton Paul Defiant, which mounted heavy armament in a rotating turret.