The Blenheim IF flew some of Fighter Command's early offensive operations, and the type soon proved vulnerable when pitted against single-seat fighters. However, for much of 1940 the Blenheim fighter squadrons provided the RAF's main long-range convoy escort and nightfighter capability. In the mid-1930s, in an attempt to capitalise on its expertise in power-operated gun turrets, the Boulton Paul Company developed the Defiant, a single-engined fighter in which all the armament was concentrated in the turret behind the pilot. Intended as a 'bomber destroyer', the Defiant had its combat debut over Dunkirk, and initially achieved some considerable success. A number of American-built aircraft called Douglas DB-7 light bombers (named Havoc by the RAF), were fitted with radar for nightfighter duties and others successfully replaced the Blenheim as night intruders. A total of 11 pilots claimed five or more victories when flying these three types to become aces, whilst no fewer than 33 who became aces claimed at least part of their scores when flying the Blenheim, Defiant or Havoc.
