Although it had originally been developed as an unarmed bomber and reconnaissance aircraft, it quickly became clear that the Mosquito design had a great deal of potential as a fighter aircraft. Work began on the fighter prototype (No. W4052) in 1940, to Air Ministry Specification F.21/40.
The prototype replaced the glass nose of the bomber/ reconnaissance version with a solid nose, containing four .303in Browning machine guns. Four 20mm cannon were located below the nose, extending back into the bomb bay. This gave the Mosquito F Mk II a very impressive punch, all concentrated in the nose.
The fighter prototype was the second Mosquito to fly, making its maiden flight on 15 May 1941. It soon became clear that the most important role for this new fighter would be as a radar equipped night fighter. The NF Mk II was equipped with the Mk IV Airborne Intercept Radar set. This needed three antennas – one arrow shaped antenna in the nose (the transmitter), just above the .303in machine guns, and one antenna at the end of each wing (the receivers). This form of radar allowed the NF Mk II to retain all eight guns carried by the F Mk II. Later radar sets would require rather larger antenna, resulting in the removal of the .303s.
The NF Mk II entered service with No. 157 Squadron on 26 January 1942. The squadron was ready to start operations by April 1942, flying its first Mosquito sortie on 3 April 1942. However, the Mosquito NF Mk II would not score its first confirmed victory until 24/25 June 1942.
The NF Mk II suffered from a few minor problems early in its career. Possibly the most serious of these was the choice of paint. At first the standard night fighter paint was used, black paint with a non-reflective rough finish. This was discovered to slow the aircraft down by around 25 mph, and so was replaced by a smooth black finish. This restored the aircraft’s speed, but made it too easy to see, especially on moon lit nights. Finally, a mix of Medium Sea Gray and Dark Green was adopted, and used for the rest of the war.
The NF Mk II was also used to fly offensive missions over occupied Europe. For this task the radar was removed, and extra fuel tanks fitted. The modified aircraft were known as NF Mk II (Special) Intruders. These aircraft were used by No. 23 Squadron to attack enemy airfields at night, starting from bases in Britain in 1942, before moving on the Malta in December 1942.
In total 494 F Mk IIs and NF Mk IIs were built. A number of them were converted for other duties, including two converted to the Photo Reconnaissance role.
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