Armstrong Whitworth Albemarle

The Armstrong Whitworth A.W.41 Albemarle was a British twin-engine transport aircraft that entered service during the Second World War.

The Albemarle was originally designed as a medium bomber, but never served in that role, instead being used for general and special transport duties, paratroop transport and glider towing, including significant actions such as Normandy and the assault on Arnhem during Operation Market Garden.

Background
Air Ministry Specification B.9/38 required a twin-engine medium bomber of wood and metal construction, that could be built by manufacturers outside the aircraft industry, and without using light alloys. The Air Ministry was concerned that if there was a war, the restricted supply of materials might affect construction of bombers.

Armstrong Whitworth, Bristol and de Havilland were approached for designs. Bristol proposed two designs - a conventional 80 ft wingspan capable of 300 mph, and a tricycle design with 70 ft span with a maximum speed of 320 mph. Both designs, known as the Type 155, used two Bristol Hercules engines. Armstrong Whitworth's AW.41 design used a tricycle undercarriage - influenced by its use in America - and was built up of sub-sections to ease manufacture by firms without aircraft construction experience. The AW.41 was designed with Rolls-Royce Merlin engines in mind, but with Bristol Hercules as an alternative ("shadow") engine.

In June 1938, mockups of both the AW.41 and Bristol 155 were examined, and new specifications B.17/38 and B.18/38 were drawn up for the respective designs. De Havilland did not submit a design. The specification stipulated 250 mph at 15000 ft economical cruise while carrying 4,000 lb (1,800 kg) of bombs. However, Bristol was already heavily engaged with other aircraft production and development, and stopped work on the 155.

Changes in policy made the Air Staff reconsider the Albemarle as principally a reconnaissance aircraft capable of carrying out bombing. Among other effects, this meant more fuel to give a 4,000 mile range. Two defensive positions were added; an upper dorsal turret, and a (retractable) ventral turret to enable downward firing. In October 1938, 200 aircraft were ordered "off the drawing board" (i.e. without producing a prototype first). The aircraft was always expected to be of use as a contingency, and to be less than ideal.

Design and development
The Albemarle was a mid-wing, cantilever monoplane with twin twin fins and rudders. The fuselage was built in three sections; the structure being unstressed plywood over a steel tube frame. The forward section used stainless steel tubing to reduce interference with magnetic compasses. It had a Lockheed hydraulically operated, retractable tricycle landing gear, with the main wheels retracting back into the engine nacelles, and the nose wheel retracting backwards into the front fuselage.

The two pilots side-by-side, a radio operator sat behind the pilots, and the navigator sat in the nose forward of the cockpit. The bomb aimer's sighting panel was incorporated into the crew hatch in the underside of the nose. In the rear fuselage were glazed panels, so a "fire controller" could coordinate the turrets against attackers. The dorsal turret was a Boulton-Paul design with four Browning machine guns. A fairing forward of the turret automatically retracted as the turret rotated to fire forwards. Fuel was in four tanks, and additional tanks could be carried in the bomb bay.

A notable design feature of the Albemarle was its undercarriage, which included a retractable nose-wheel (in addition to a semi-concealed "bumper" tail-wheel). It was the first British-built aircraft with this configuration to enter service with the Royal Air Force.

The original bomber design required a crew of six including two gunners; one in a four-gun dorsal turret and one in a twin-gun ventral turret. However, only the first 32 aircraft, the Mk I Series I, were produced in this configuration, and they were only used operationally in the bomber role on two occasions. That was because the Albemarle was considered inferior to other aircraft already in service, such as the Vickers Wellington. All subsequent aircraft were built as transports, designated either "General Transport" (GT) or "Special Transport" (ST).

When used as a paratroop transport, 10 fully armed troops could be carried. The paratroopers were provided with a dropping hatch in the rear fuselage, and a large loading door in the fuselage side.

The entire production run of 600 Albemarles was assembled by A.W. Hawksley Ltd of Gloucester, a subsidiary of the Gloster Aircraft Company formed for the purpose of the construction of the Albemarle. Gloster was a part of the Hawker Siddley group which included Armstrong Whitworth. Individual parts and sub-assemblies for the Albemarle were produced by about 1,000 subcontractors.

Operational history
The first Albemarle (P1360) first flew on 20 March 1940 at Hamble Aerodrome, where it was assembled by Air Service Training, and was the first of two prototypes built by Armstrong Whitworth. To improve take-off, a wider span (77 from 67 ft) wing was fitted after the 8th aircraft. Plans for using it as a bomber were dropped due to delays in reaching service, it was not an improvement over current medium bombers (such as the Vickers Wellington) and its obvious shortcomings compared to the four-engined heavy bombers about to enter service, but it was considered suitable for general reconnaissance.

The first squadron to operate the Albemarle was No. 295 at RAF Harwell in January 1943. Other squadrons to be equipped with the Albemarle were No. 296, No. 297 and No. 570. Other RAF squadrons operated small numbers of the aircraft. On 9 February 1943, the first operational flight was a 296 Squadron Albemarle which dropped leaflets over Lisieux in Normandy. Albemarles took part in many of the major British airborne operations, such as the invasion of Sicily and of Normandy and the assault on Arnhem during Operation Market Garden.

In October 1942, the Soviet Air Force placed a contract for delivery of 200 Albemarles. No. 305 Ferry Training Unit was set up at RAF Errol near Dundee to train Soviet aircrews. During training, one aircraft was lost with no survivors. On 3 March 1943, the first Soviet AF Albemarle flew successfully from Scotland to Vnukovo airfield, followed by 11 more. Two aircraft were lost over the North Sea; one to German interceptors, and the other unaccounted for. Tests of the surviving Albemarles revealed their weaknesses as transports (notably the cramped interior) and numerous technical flaws; in May 1943, the Soviet government put further deliveries on hold, and eventually cancelled them in favour of abundant American Douglas C-47 Skytrains. The Soviet camp at Errol field continued until April 1944; apparently the Soviet command hoped to secure de Havilland Mosquito deliveries. Twelve Soviet Albemarles served for about two years; at least two were lost in accidents. Surviving aircraft were retired at the end of 1945.

The pinnacle of the aircraft's career was a series of operations for D-Day on 5 June 1944. 295 and 296 Squadrons sent aircraft to Normandy with the pathfinder force, and 295 Squadron claimed to be the first squadron to drop Allied troops during Operation Overlord. On 6 June 1944, four Albemarle squadrons and the operational training unit all sent aircraft during Operation Tonga; 296 Squadron used 19 aircraft to tow Airspeed Horsas, 295 Squadron towed 21 Horsas, although it lost six in transit, 570 Squadron sent 22 aircraft with ten towing gliders, and 42 OTU used four aircraft. For Operation Mallard on 7 June 1944, the squadrons towed 220 Horsas and 30 Hamilcars to Normandy.

On 17 September 1944, during Operation Market Garden at Arnhem, 54 Horsas and two Hadrian gliders were towed to the Netherlands by 28 Albemarles of 296 and 297 squadrons; 45 aircraft were sent the following day towing gliders.

Of the 602 aircraft delivered, 17 were lost on operations, and 81 lost in accidents. The last Royal Air Force unit to operate the type was the Heavy Glider Conversion Unit, which replaced the Albemarles with Handley Page Halifaxes in February 1946, and the type was retired from operational units.

Variants
Over the course of its production life, a number of variants of the Albemarle were built:
 * ST Mk I - 99 aircraft
 * GT Mk I - 69
 * ST Mk II - 99
 * Mk III - One prototype only.
 * Mk IV - One prototype only.
 * ST Mk V - 49
 * ST Mk VI - 133
 * GT Mk VI - 117

Most Marks were divided into "Series" to distinguish differences in equipment. The ST Mk I Series 1 (eight aircraft) had the four gun turret replaced with hand operated twin-guns under a sliding hood. As a special transport, a loading door was fitted on the starboard side; the rear fuel tank was removed. The 14 ST Mk I Series 2 aircraft were equipped with gear for towing gliders. The Mk II could carry 10 paratroops and the Mk V was essentially the same but with a fuel jettison capability. All production Albemarles were powered by a pair of 1,590 hp (1,186 kW) Bristol Hercules XI radial engines.

The Mk III and Mk IV Albemarles were development projects for testing different powerplants; the former used the Rolls-Royce Merlin III, and the latter used the 1,600 hp (1,190 kW) Wright Double Cyclone.

Operators
Royal Air Force Aircraft were also operated for tests and trials by aircraft companies, the Royal Aircraft Establishment, and Aeroplane and Armament Experimental Establishment. One was operated by De Havilland Propellers for research into reversing propellers.
 * Twelve aircraft were exported to the Soviet Union (two more lost in transit).
 * Transport arm of 1st Air Division, later 10th Guards Air division (to 1944); naval air units until retirement in 1945.
 * Transport arm of 1st Air Division, later 10th Guards Air division (to 1944); naval air units until retirement in 1945.
 * No. 161 Squadron RAF - Albemarle I from October 1942 to April 1943 at RAF Tempsford.
 * No. 271 Squadron RAF operated one aircraft at Doncaster between October 1942 and April 1943.
 * No. 295 Squadron RAF - Albemarle I from November 1943 to July 1944 at RAF Hurn and then RAF Harwell. Albemarle II from October 1943 to July 1944 at RAF Hurn and then RAF Harwell. Albemarle V from April 1944 to July 1944 at RAF Harwell.
 * No. 296 Squadron RAF - Albemarle I from January 1943 to October 1944 at RAF Hurn, RAF Stoney Cross including operations in North Africa. Albemarle II from November 1943 to October 1944 at RAF Hurn and then RAF Brize Norton. Albemarle V from April 1944 to October 1944 at RAF Brize Norton. Albemarle VI from August 1944 to October 1944 at RAF Brize Norton.
 * No. 297 Squadron RAF - Albemarle I from July 1943 to December 1944 at RAF Thruxton, RAF Stoney Cross and then RAF Brize Norton. Albemarle II from February 1943 to December 1944 at RAF Stoney Cross and then RAF Brize Norton. Albemarle V from April 1944 to December 1944 at RAF Brize Norton. Albemarle VI from July 1944 to December 1944 at RAF Brize Norton.
 * No. 511 Squadron RAF - Albemarle I from November 1942 to March 1944 at RAF Lyneham.
 * No. 570 Squadron RAF - Albemarle I from November 1943 to August 1944 at RAF Hurn and then RAF Harwell. Albemarle II from November 1943 to August 1944 at RAF Hurn and then RAF Harwell. Albemarle V from May 1944 to August 1944 at RAF Harwell.
 * No. 1404 Flight RAF used three aircraft at RAF St Eval from September 1942 to March 1943
 * No. 1406 Flight RAF used two aircraft at RAF Wick from September to October 1942.
 * No. 13 Operational Training Unit RAF at RAF Finmere (two aircraft between October 1942 and April 1943)
 * No. 42 Operational Training Unit RAF at RAF Ashbourne from September 1943 to February 1845.
 * Heavy Glider Conversion Unit at RAF Brize Norton and RAF North Luffenham from January to April 1943 and August 1944 to October 1944 when it became No. 21 Heavy Glider Conversion Unit.
 * No. 21 Heavy Glider Conversion Unit at RAF Brize Norton from 1944, moved to RAF Elsham Wolds in December 1945 and withdrew the last operational Albemarles in February 1946.
 * No. 22 Heavy Glider Conversion Unit at RAF Keevil and RAF Blakehill from October 1944 to November 1945.
 * No. 23 Heavy Glider Conversion Unit at RAF Peplow from October to December 1944.
 * No. 3 Glider Training School operated eight Albemarles at RAF Exeter between January and August 1945.
 * No. 301 Ferry Training Unit operated four Albemarles at RAF Lyneham from November 1942 to April 1943.
 * No. 305 Ferry Training Unit bases at RAF Errol from January 1943 to train Soviet Air Force crews, disbanded in April 1944.
 * Torpedo Development Unit at Gosport used one aircraft between April and September 1942
 * Telecommunications Flying Unit at RAF Defford used one aircraft during May 1943,
 * Airborne Forces Experimental Establishment at RAF Ringway and RAF Sherburn-in-Elmet between May 1942 and October 1944.
 * Coastal Command Development Unit used two aircraft at RAF Tain between September and December 1942.
 * Central Gunnery School at RAF Sutton Bridge used one aircraft between September and November 1942.
 * Bomber Development Unit used three aircraft at RAF Gransden Lodge between August and November 1942.
 * Operation Refresher Training Unit at RAF Hampstead Norris from May 1944 to February 1945