The Boulton Paul Defiant was an early World War II fighter aircraft of the Royal Air Force built by Boulton Paul Aircraft Ltd. Amongst pilots it had the informal nickname "Daffy". The Boulton Paul Defiant, went into action for the first time during operations against the Nazi invaders of Holland. The design of the aircraft was an attempt to overcome the need to point the nose of a fighter at its target in order to bring the guns to bear. Instead of forward-facing guns, the Defiant was fitted with a powered dorsal turret equipped with four 0.303 in (7.7 mm) Browning machine guns. In theory, the Defiant would approach an enemy bomber from below or beside and destroy it with a concentrated burst of fire. The concept was similar to the successful World War I Bristol Fighter, and the Fleet Air Arm's contemporary Blackburn Roc, but in practice the Defiant was highly vulnerable to the more agile Luftwaffe Bf 109 escort fighters. It was later used in the night fighter role where it had considerable success against Luftwaffe bombers, before it was phased out of combat operations.