H.P.57 Halifax I
Construction was ordered in January 1937, and after the Munich Crisis production orders were massively increased. While Avro persevered with their Vulture engine Manchester, HP were able to skip directly to the Merlin - but all that meant was that the initial teething problems of a new design would continue to dog the reputation of the Halifax for all its production.
The prototype Halifax first flew in the opening days of the War, and design and production was kept as secret as possible. The first protype was flown without armorment, but the second protoype was completed fully configured. Dorsal and ventral turrets were not installed, but waist guns were installed on either fuselage side.
The first production Halifax was kept as a development aircraft, and became the most heavily armed Halifax I when testing dorsal and ventral turrets in addition to the standard gun positions.
The first operational sortie for the Halifax was on 10/11 March 1941. The secrecy of the design was such that the first Halifax casualty occurred on that first raid, and was an aircraft shot down by a British night fighter unaware of the existence of the Halifax.
Structural modifications allowed a greater all-up weight, and these aircraft were designated Halifax B.I series 2 aircraft. Initially the aircraft were fitted with retractable tailwheels, but they were troublesome and soon discarded.
The next modification involved the addition of a fuel dump system.
A Halifax B.I was the test aircraft for the H2S radar system, and was the first aircraft to fly with H2S.