B Mk II Series 1 (HP 59)
The main change made to the Mk II Halifax was the use of the 1,280 hp Merlin XX engine, giving a significant performance boost over the Mk I. Amongst the improvements was a 3,000 feet increase in the service ceiling, bringing it up to 21,000 feet. The majority of Mk II Series I aircraft also had a new dorsal turret, the Boulton Paul C, in place of the beam guns that could be carried on the Mk I. The Mk II entered service in October 1941.
B Mk II Series 1 (Special)
The Mk II Series 1 Special was the result of concerted efforts at Boscombe Down to reduce the weight and drag of the Halifax, to improve performance. The most obvious visual change was the removal of the front gun turret, and its replacement by a smooth fairing, known as the “Z Fairing” due to the shape of the framework used to attach it to the aircraft. This was often combined with the removal of the dorsal turret, and increased the speed of the Halifax by 16 mph. As a indication of how significant small changes could be, the removal of one layer of rough finish paint (RDM2 black) from the Halifax increased the top speed by another 5 mph! The Mk II (Special) entered squadron service in the autumn of 1942. The Mk II (Special) was produced in parallel with the Mk V Series 1 (Special), which was identical apart from its undercarriage.
B Mk II Series 1a
The Mk II Series 1a entered service during June 1943. It saw a final refinement of the Halifax’s nose. The Z-fairing of the Series 1 Special was replaced by a clear plastic one piece nose cone. This gave the bomb aimer much more space. It also allowed the fitting of a single Vickers .303 K gun, mostly for morale purposes. The Boulton Paul C turret was also replaced by the Boulton Paul A Mk VIII turret, which was rather more streamlined. The Mk II Series 1a also saw another new engine appear, this time the Merlin 22, capable of providing 1,480 hp at 12,500 ft.
A final significant change came during the production run of the Mk II Series 1a. Earlier versions of the Halifax had demonstrated a dangerous tendency to spin at low speeds. This was tracked down to the design of the rudder and the entire tail. The response was to replace the original tail design with a new “D” shaped fin, increasing the size of the control surfaces and reducing the danger. The Mk II Series 1a also had an equivalent Mk V Series 1a.
GR MK II Series 1 (Special)
Coastal Command received its first twenty Halifax B Mk IIs on 18 October 1942. These aircraft were used on anti-submarine patrols over the Bay of Biscay, the main route used by the U-boats on their way to and from their French bases.
The Halifax received a number of modifications for naval work, one of which was the fitting of ASV Mk III radar. The radar equipment was located in a cupola underneath the rear fuselage of the aircraft. The majority of Coastal Command Halifaxes were radar equipped by May 1943.
Its wing mounted bomb bays were ideally suited for anti-submarine work. Coastal Command modified their GR Mk IIs to carry extra fuel tanks in the main bomb bay, and six 600lb depth bombs in the wings. In this configuration the Halifax had a maximum endurance of sixteen hours, although for operational use that was reduced to no more than thirteen hours.
GR Mk II Series 1A
The main change made to the Mk II Series 1A in Coastal Command was the replacement of the Vickers .303 K gun with a .5in Browning machine gun. This was required because later U-boats carried a formidable array of anti-aircraft guns, and tended to stay on the surface to fight it out with attacking aircraft.