The Boulton Paul Defiant was a British interceptor aircraft that served with the Royal Air Force (RAF) during the Second World War. The Defiant was designed and built by Boulton Paul Aircraft as a "turret fighter", without any forward-firing guns. It was a contemporary of the Royal Navy's Blackburn Roc. The concept of a turret fighter related directly to the successful First World War-era Bristol F.2 Fighter.
In practice, the Defiant was found to be reasonably effective as a bomber–destroyer, but vulnerable to the Luftwaffe's more agile, single-seat Messerschmitt Bf 109 fighters. Lack of forward armament proved to be a major weakness in daylight combat and its potential was only realized when it switched to night combat.