The Df. 4 was a British fighter aircraft that was developed and used during World War II. It was a single-seat, single-engine fighter, known for its high speed and maneuverability. The Df. 4 was initially intended to be used as a day fighter, but was later adapted to perform night-fighting duties. It was a highly effective fighter aircraft, and served with distinction in the Battle of Britain and other major engagements of the war.