The Avro Type 694 Lincoln is a British four-engined heavy bomber, which first flew on 9 June 1944. Developed from the Avro Lancaster, the first Lincoln variants were initially known as the Lancaster IV and V; these were renamed Lincoln I and II. It was the last piston-engined bomber operated by the Royal Air Force (RAF); the later Avro Shackleton, though piston-engined, served in maritime patrol rather than bomber roles.
The Lincoln attained operational status in August 1945. It had been initially assigned to units of the Tiger Force, a Commonwealth heavy bomber force which had been intended to play a role in the Japan campaign in the closing stages of the Second World War, but the war ended before the Lincoln could participate. Production of the type proceeded and the type was adopted in quantity, complementing and progressively replacing the Lancaster in RAF service during the late 1940s.
The Lincoln was deployed on operations during the 1950s. RAF squadrons equipped with the type fought against guerrilla fighters during the Mau Mau Uprising in Kenya; the RAF and the Royal Australian Air Force (RAAF) also operated the Lincoln during the Malayan Emergency. The type also saw significant peacetime service with the RAF, RAAF and the Argentine Air Force. Lincolns were also operated in civil aviation, including use as aerial test beds for aero-engine research.
In RAF service, the Lincoln was replaced by a new generation of bombers using jet propulsion. In 1967 the last Lincoln bombers in service, in Argentina, were retired.
Design and development
Origins
The Avro Lincoln originated from a design produced by Roy Chadwick as a development of the earlier Lancaster bomber which had been produced with the purpose of conforming with the requirements of the Specification B.14/43. Known initially as the Lancaster IV and Lancaster V, the envisioned aircraft, while considerably similar to the Lancaster, had numerous improvements such as the adoption of stronger, longer span, higher aspect ratio (10.30 compared with 8.02) wings, and two-stage supercharged Rolls-Royce Merlin 85 engines fitted within Universal Power Plant (UPP) installations.
thumb|Royal Air Force Lincoln B.2 used by [[Napier & Son|Napier's for icing research work until 1967 (1966)]]
The prototype Lancaster IV, later renamed the Lincoln I, was assembled by Avro's experimental flight department at Manchester's Ringway Airport. According to aviation author Kev Delve, development of the Lincoln had proceeded relatively smoothly. Testing of the prototype quickly proved it to have favourable flight characteristics. A new emphasis was soon placed on 'quality over quantity' during the rationalisation process, seeking to employ fewer but more capable aircraft to perform their envisioned roles; while there was no longer any urgency in bringing new types of aircraft into service, limited procurement of equipment that fell within this ethos did proceed. Along with two additional Lincoln (Mk I and Mk II) aircraft on loan from the RAF, the type was briefly evaluated postwar by the RCAF. The Lancaster V/Lincoln II differed mainly in that it was fitted with Merlin 68A engines.
Prior to the Lincoln being developed, the Australian government had already formulated plans for its Department of Aircraft Production (DAP), later known as the Government Aircraft Factory (GAF), to construct the earlier Lancaster Mk III. In its place, it was decided to proceed with manufacturing a variant of the Lincoln I, re-designated the Lincoln Mk 30, to replace the Consolidated Liberators. This model was manufactured between 1946 and 1949, and is the largest aircraft ever constructed in Australia. Orders for a total of 85 Mk 30 Lincolns were placed by the RAAF, although only 73 were produced.
thumb|left|Lincoln A73-20 during a test flight. Both starboard engines have their propeller blades [[Propeller (aeronautics)#Feathering|feathered]]
The first five Australian examples (A73–1 to A73–5), were assembled at Fishermans Bend using a large proportion of imported British-made components. On 17 March 1946, A73-1 conducted its début flight; the first entirely Australian-built Lincoln, A73-6, was formally delivered in November 1946. The Mk 30 initially used four Merlin 85 engines, this arrangement was later changed to a combination of two outboard Merlin 66s and two inboard Merlin 85s. A further improved later version, the Lincoln Mk 30A, had four Merlin 102s.
During the 1950s, the RAAF modified some of their Mk 30 aircraft for anti-submarine warfare (ASW) re-naming them Lincoln GR.Mk 31. These examples had a longer nose to house acoustic submarine detection gear and its operators, larger fuel tanks to provide the aircraft with a 13-hour flight endurance, and a modified bomb bay to accommodate torpedoes. According to pilot feedback, the Lincoln Mk 31 was particularly difficult to land at night, as the bomber had a tailwheel undercarriage and the long nose obstructed the pilot's view of the runway. In 1952, 18 aircraft were rebuilt to this standard, and were reallocated new serial numbers.
Further aircraft were also derived from the Lincoln. A dedicated maritime patrol aircraft, designated the Avro Shackleton, was developed for the RAF and the South African Air Force (SAAF). Avro decided to develop a commercial airliner, known as the Tudor, which used elements of the Lincoln, such as its wings, in combination with various new elements, such as the adoption of a pressurised fuselage, to perform passenger operations.
Operational history
Royal Air Force
thumb|Lineup of the first operation of [[No. 1 Squadron RAAF|No. 1 Squadron, Royal Australian Air Force at RAF Tengah, Singapore, August 1950]]
During 1945, the RAF received its first Lincoln, which was delivered to 57 Squadron based at RAF East Kirkby, Lincolnshire. In August 1945, 75 (New Zealand) Squadron began to re-equip with the Lincoln at RAF Spilsby, Lincolnshire. The New Zealand squadron had received just three aircraft prior to VJ Day, and was disbanded quickly thereafter. Small numbers remained in use with 7, 83 and 97 Squadrons until the end of 1955, at which point the type was phased out, having been replaced by the first of the V bombers.
During the 1950s, RAF Lincolns participated in operations in Kenya against Mau-Mau insurgents. During this action, they were operated from Eastleigh. The Lincoln was also deployed to Malaya during the Malayan Emergency, where it was used against insurgents aligned to the Malayan Communist Party. In Malayan theatre, RAF Lincolns were operated from Changi Air Base and Tengah Air Base. In excess of 3,000 sorties were flown during their -year deployment, during which half a million pounds of bombs dropped, 85 per cent of the total bomb tonnage dropped during the Malayan emergency.
In November 1955, four Lincolns of 7 Squadron were detached for duties in British territories in the Middle East. In Bahrain, they carried out border patrols of the Trucial States at the time of the Buraimi dispute. When 7 Sqn was disbanded in December 1955, the four detached crews and aircraft became 1426 Flight, officially a photographic reconnaissance unit. It was later sent to Aden, carrying out patrols in the lead-up to the Aden Emergency.
As the RAF Lincolns became unserviceable, primarily due to wear and tear, they were replaced by jet-powered aircraft. The Lincolns of Bomber Command were phased out from the mid-1950s and had been replaced by jet bombers by 1963. The last Lincolns in RAF service were five operated by 151 Squadron, Signals Command, at RAF Watton, Norfolk, which were retired on 12 March 1963. The adoption of the Lincoln effectively gave Argentina the most powerful bombing force in South America. In 1947, the type entered service with I Grupo de Bombardeo of V Brigada Aérea. At the beginning of 1965, eleven of these remained in operational use; most of them were retired during the next year. In 1967 the last Lincolns were retired.
The Argentine aircraft were used in bombing missions against domestic rebels. Lincolns were deployed during an attempted military coup in September 1951; the type was also used by both the government and rebel forces during the 1955 Revolución Libertadora coup which deposed Argentine President Juan Perón. In 1948, one of the bombers was returned to Avro for modification at RAF Langar in Nottinghamshire to allow it to operate these Antarctic support flights; the changes included the addition of Lancastrian nose and tail cones, additional fuel tanks, and removal of armament; the aircraft became the first Avro Lincolnian.
Use in aero-engine research
thumb|Avro Lincoln testbed G-37-1 at the Farnborough SBAC Show in 1956, flying solely on its nose-mounted Rolls-Royce Tyne
Lincolns were frequently employed as testbeds in new jet engine development. RF403, RE339/G and SX972 flew with a pair of Armstrong Siddeley Python turboprops outboard in place of the Merlins, and was used for the ballistic casing drop-test programme for the Blue Danube atomic weapon. SX972 was further modified to fly with a pair of Bristol Proteus turboprops. RA716/G had a similarly placed pair of Bristol Theseus turboprops and later also flew with Rolls-Royce Avon turbojets replacing the pair of turboprops. Lincoln Test Bed RF530 kept its Merlins but had a Napier Naiad turboprop in the nose. It later flew, bearing the civilian "Class B" test registration G-37-1, with a similarly placed Rolls-Royce Tyne which it displayed at the 1956 Society of British Aircraft Constructors (SBAC) show, making a low level flypast on just the nose Tyne, the four Merlins being shut down and propellers feathered.SX973 had a Napier Nomad diesel turbo-compound installed in a similar nose-mounted installation. RA643 flew with a Bristol Phoebus turbojet in the bomb bay, and SX971 had an afterburning Rolls-Royce Derwent mounted ventrally.
Commercial service
A pair of Lincoln IIs were operated by D. Napier & Son Ltd. for icing research from 1948 to 1962. A transport conversion of the Lincoln II, using the streamlined nose and tail cones of the Lancastrian and a ventral cargo pannier was known as the Avro 695 Lincolnian.
;Lincoln II
:Long-range bomber version for the RAF. Powered by four Rolls-Royce Merlin 66, 68A and 300 inline piston engines. Built by Avro, Armstrong-Whitworth and Vickers-Metropolitan.
;Lincoln III
:The Lincoln III was intended to be a maritime reconnaissance, anti-submarine warfare aircraft. The aircraft later became the Avro Shackleton.
;Lincoln IV
:Lincoln II converted to Merlin 85 power.
;Lincoln Mk 15 (B Mk XV)
:This designation was given to one aircraft, built by Victory Aircraft in Canada.
;Lincoln Mk 30
:Long-range bomber version for the RAAF.
- No. 9 Squadron RAF 1946–52 at RAF Binbrook, then converted to the English Electric Canberra.
- Australia
- Lincoln II RF342 is in storage for future restoration at the Australian National Aviation Museum, Melbourne.
Specifications (Lincoln I)
thumb|Cockpit of an Avro Lincoln
thumb|Bomb bay of a preserved Lincoln