On 17 Nov 1941, the first Mosquito bomber (B Mk IV) entered service. By mid-May 1942, only eight were operational, all with 105 Squadron (GB code, see picture).
RAF Bomber Command was eager to test this fast bomber in combat. Tests showed it had an amazing performance. A max speed of 620 km/h at altitude and good acceleration allowed it to escape easily from night fighters. Even during daylight, the risks were lessened because the Fw 190A-2’s top speed was 630 km/h, giving it a small speed margin to catch the Mosquito if its crew was attentive enough to detect the German fighters from a long distance. Some reports indicated that at sea level, the speed of both aircraft was almost identical, so the German fighter could only catch the fast British bomber if it dived from altitude at the proper time.
On 31 May 1942, the Mosquito Mk IV made its operational debut as a bomber (the aircraft had been used as a photographic reconnaissance aircraft for some months already). At dawn, four were sent to bomb and photograph Cologne from 24,000 feet, which had just been bombed by 1000 bombers.
Two of the Mosquitos were shot down by Flak (which demonstrated the danger the German Flak posed to even fast aircraft flying at those altitudes).
Two days later, four Mosquitoes from 105 squadron and two from 139 squadron were sent in broad daylight to attack a U-boat construction yard in Flensburg (the first squadron from low-level and the second from high-level). Two of the Mosquitoes from 105 squadron failed to return. Some sources indicate Fw 190s shot down both, while others indicate that the 190s bagged one while the other was destroyed by light Flak.
The Mosquito, nevertheless, eventually proved to be one of the most successful British aircraft of the war.