The interception of these massive aircraft, although difficult due to their high speed and low visiblility was largely entrusted to the Mosquito Night Fighter NF Mk.XIII and NF Mk.XVII variants. It was in 1941 that the RAF began development of a night after version of the all-wood Mosquito. The first was the NF Mk.II, which was equipped with an Mk.IV Airborne Intercept Radar on the nose. However, it limited range at low altitudes proved problematic versus the low-altitude, high speed attackers. For this reason, the Mosquito NF Mk.II came to be equipped with a new centimetric radar known as the A.I. Mk.VIII. The official designation of this aircraft was NF Mk.XII. The new A.I. Mk.VIII radar was also fitted to an airframe based on the Mosquito FB Mk.VI, inside a "bullnose" radome on the nose, resulting in the NF Mk.XIII. This Mosquito boasted reinforced wings, could carry 50 gallon drop tanks, and was powered by two of either the Merlin 21 or 23 engines. The sting of this Moasquito came from four 20mm Hispano Cannons installed just under the nose. Later, the lightweight and improved American-made CR-720 radar was mounted on the NF Mk.XVII version of the Mosquito, which would enter air combat soon after.