McMehen, Robert John (Flying Officer)

Introduction

The Halifax was the most common heavy bomber employed by Canadians in WW2 -- over 70% of Canadain bomber crews were asigned to the Halifax Bomber. Canada's highest losses of airmen in Halifaxs:

The Halifax was available and flying in 1940. The Lancaster was not available in any significant numbers until mid 1942.

Manufacturers

Variants

The Mark IV was never built.

Engines

The Merlin XX and 22 are equivalents.

Aircraft Origin

The origins of the Halifax lay in the twin-engine H.P.56 proposal of the late 1930s, produced in response to the British Air Ministry's Specification P.13/36 for a medium bomber for 'world-wide use'. Handley Page initially envisioned a design using of two Rolls-Royce Vulture X-24 engines, but as the airframe design developed and the Vulture's shortcomings became more apparent, the twin-engine H.P.56 evolved into the larger and more capable H.P.57 Halifax powered by four Rolls-Royce Merlin engines. The first flight took place at RAF Bicester on 25 October 1939, the aircraft entering RAF service just over a year later on 13 November 1940.

Ventral Turret

In service it quickly became apparent that the Boulton Paul Type K ventral turret as fitted to early Mk.I aircraft with its twin 0.303-inch calibre machine guns was next to useless, and the turret was replaced on later Mk.Is and early H.P.59 Mk.IIs by two beam gun positions each with twin Vickers Type K 0.303-inch machine guns. In turn the beam guns were also found to be redundant and were soon discontinued.

Rudder Overbalance

However, much more serious deficiencies became apparent following the introduction of the heavier Halifax Mk.II and H.P.63 Mk.V with its Dowty undercarriage and hydraulic system. In addition to poor overall performance, the number of aircraft lost in mysterious circumstances began to rise alarmingly. Following a protracted investigation, the cause was eventually traced to irrecoverable loss of control due to rudder overbalance and was cured by the introduction of the distinctive large rectangular D-Type fins and rudders.

Performance Improvements

Loss of performance in the Mk.II & V was addressed by a number of means including replacement of the front turret by a metal and later Perspex one-piece nose, and replacement of the bulbous drag-inducing Boulton Paul two gun Type C mid-upper turret with the lower profile four gun Type A turret. Improved engine cowlings, more powerful Merlin engines and a general airframe clean-up also helped to somewhat restore the Mk.II and V's performance.

Bristol Hercules Engines

A further improvement of the Merlin-powered Halifax known as the Mk.IV was planned but never built, the design featuring increased wingspan and even more powerful Merlins in completely redesigned and repositioned nacelles. However, a study of the advantages of the sleeve valve 14-cylinder Bristol Hercules radial engine convinced Handley Page to discontinue Merlin Halifax development and instead introduce the Hercules-powered H.P.61 Mk.III. Initially built with 98 ft 10 in wingspan, the Mk.III soon received the still-born Mk.IVs 104 ft 2 in wings, the new mark proving to be the turning point in the Halifax's fortunes.

Later in the war, the Halifax H.P.63 Mk.VI with more powerful fuel-injected Hercules 100 series engines, improved flying controls and systems proved to be the pinnacle of wartime Halifax development, the mark outperforming the Lancaster in some respects. Unfortunately, the Hercules 100 wasn't available in sufficient quantities, and so the Mk.VI airframe was also built with lower powered Hercules XVIs as the Halifax H.P.63 Mk.VII.

.5-inch (50 calibre) Machine Guns

The advantages of the 0.5-inch calibre machine gun over the 0.303-inch calibre were well known and following a protracted turret development programme, some Mk.VII & IX aircraft were fitted with Boulton Paul Type D rear turrets with twin 0.5-inch guns. The final bomber variant was the H.P.71 Mk.IX. Like the earlier variants the IX could also be used for glider towing and paratrooping, and for the latter task the Mk.IX featured an elongated and repositioned paratroop exit aperture.

A - Glider Tug and Transport

B - Bomber

C - Cargo and Passenger

GR - Coastal Command

Met - Meteorological

Series Designations

In addition to the basic mark number the Halifax Mk.I, II & V also had a series number eg. series 1, series 1a, series 2. The series number is not included in our database because it is not easily or accurately determined.

Mk.II & V

The basic series number of all the rest of the Mk.IIs & Vs was Series 1. Some early production airframes were built as straight Series 1s and later modified, and some later production airframes were built with one or both of the key suffix-changing modifications already incorporated. Regardless of whether the change/s occurred during or post-manufacture, a suffix was supposed to be added to the series number when the following changes occurred:

1. Replacement of the front turret with the one-piece metal fairing (Mod.398 aka Tollerton nose, Tempsford nose or Z-fairing) - this added the suffix (Special) after the series number i.e. Series 1 (Special).
2. Installation of Merlin 22 engines and Morris radiators along with modified engine cowlings - this added the letter 'A' to the series number i.e. Series 1A.

However

1. Some late production Mk.II Series 1 (Specials) were fitted with Morris radiators and Merlin 22s but retained the designation Series 1 (Special).
2. Some Series 1 aircraft were fitted with the previous type of Gallay radiators but were designated as Series 1A.
3. Aircraft with the Mod.452 Perspex nose but without Morris radiators/Merlin 22s were not Series 1A, and the actual designation of such aircraft i.e. Series 1 or Series 1 (Special) is unknown.

NOTE - In period as now, it was widely but incorrectly believed that an aircraft became a 1A when the one-piece Perspex nose was added, but an airframe became a Series IA only when Merlin 22 & Morris radiators were installed - addition of the one-piece Perspex nose (and the large D-Type fins) made no change to the series suffix.

To add to the confusion production records are not only incomplete but sadly in a great many instances they also do not record whether a particular airframe was a Series 1, Series 1 (Special) or Series 1A. And if that wasn't enough many aircraft were field modified and the modification/s were not recorded, which of course means that many airframes could and did start life without a series suffix and gain one later when the engine or nose type changed, yet the records don't reflect the changes!

The bottom line is that unfortunately it's impossible to list the series/engine sub-model breakdowns of the Mk.II & V Series 1 aoircraft. Really the best that can be said is that early Mk.IIs and Vs had Merlin XXs and the later ones had Merlin 22s.

Meteorological Variant

Predicting the weather was a significant problem. The weather generally flows west to east in the northern hemisphere, so ascertaining the weather as far out as possible in the Atlantic Ocean gave indications of future weather events in Britain and on the continent.

The main variant was the MET V which looked very similar to a Coastal Command GR Mk.V. The aircraft themselves were fitted with very sensitive air temperature and humidity measuring equipment, plus radio altimeters to allow the crews to fly very accurately at selected altitudes, and they also carried an extra crew member who recorded the weather data. Towards the end of the war the Halifax MET V was supplemented by the MET III and VI.

From airfields located on the west coast of the UK including Tiree on the Isle of Skye, Stornoway on the Isle of Lewis, Brawdy in Wales and Chivenor in Devon the aircraft regularly flew extremely long duration meteorological reconnaissance flights over the Atlantic.

The weather forecasts used for D-Day planning were partly based on data provided by the MET Halifax squadrons.

Specs not available