H.P.59 Halifax II
The continuous fine-tuning process to get the relatively poor performing Halifax to fulfil its potential were continued with aerodynamic improvements into the Mk.II series.
The initial B.II's were actually still identical to late model B.I's. As production developed the Lockheed Hudson-style dorsal turrets were installed and the rear antenna masts removed.
To counter the glowing exhausts which were considered to be too visible for a night bomber asbestos shrouds over the exhausts were trialed.
As the Halifax's role was not just bomber, but also as a transport Halifaxes were used to support SOE and partisan activity in captured territory. Not being bombers these aircraft had reduced defensive armament to allow greater speed and range. The nose turret was removed and replaced with the variously named Tollerton/Tempsford Z-nose, creating the B.II (special).
Experience had shown that defense against frontal fighter attacks was not required for bombers, and some aircraft were initially modified in the field to have the bulkw,drag-inducing nose turrets removed. Although initially labeled B.IIZ, common usage has led to all Z-nose aircraft being referred to as B.II(special).
To increase the defensive armament the four-gun Defiant-style turret was adopted. Initially mounted raised, later aircraft had a more aerodynamic lowered positioning.
Some aircraft were allocated to Coastal Command as GR.II's (General Reconnaissance). Most aircraft were equipped with the naval version of H2S, the ASV Mk.III.
Further streamlining the Halifax nose led to the complete recontouring of the nose, rather than just removing the turret, with a further revised model becoming the B.II series 1A (HP seemed to be rather reticent about changing the model numbers). Additional aerodynamic refinement was devoted to the Halifax's inherent directional stability problem. It was determined that disturbed airflow from the nacelles was to blame, and an extended nacelle was successfully trialed on the series 1A testbed - although this modification was not carried forward into production aircraft.
The revised nose contour was now filled with a glazed nose, mounting a single Vickers K gun. The gun was referred to by crews as a "scare gun" as it was completely underpowered for defense, but with tracer ammunition attacking fighters were unaware of the gun's impotence.
Series 1A aircraft were also allocated to Coastal Command. For better action against U-boats, the scare gun was replaced with a heavier weapon, necessitating additional strengthening on the gun mountings.
An alternative method of correcting the directional stability problem was by reworking the shape of the rudder. The definitive rectangular rudder, once the design was finalised, was used on new build aircraft and retrofitted onto aircraft already in service.
Continuing aerodynamic testing revealed that the root cause of the Halifax's poor performance was interferance drag from the mounting position of the engines. An alternate Lancaster-style low slung mounting was trialed for the B.II series 2 prototype, however official interest in further reworking the Merlin Halifax had waned, and design and production was instead transferred to the radial-engined B.III.
As a final post-script to the B.II several aircraft that had been returned for scrapping with their squadron re-equipping with more modern bombers, were instead not scrapped. They were instead unofficially converted to a freighter configuration for shipping disassembeled Spitfires. The bomb bay was removed and solid metal plates placed on their side, to provide sidewalls for the fighters to be underslung. These aircraft were the last flying B.II's.