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The Avro Lancaster is a British four-engined Second World War heavy bomber designed and built by Avro for the Royal Air Force. It first saw active service with RAF Bomber Command in 1942 and, as the strategic bombing offensive over Europe gathered momentum, it became the main heavy bomber used by the RAF, the RCAF, and squadrons from other Commonwealth and European countries serving within the RAF, overshadowing its close contemporaries the Handley Page Halifax and Short Stirling.
A long, unobstructed bomb bay meant that the Lancaster could take even the largest bombs used by the RAF, including, the 4,000 lb, 8,000 lb, or 12,000 lb Blockbusters, loads often supplemented with smaller bombs or incendiaries. The versatility of the Lancaster was such that it was chosen to equip 617 Squadron, and was modified to carry the Barnes Wallis designed Upkeep "Bouncing bomb" for Operation Chastise, the attack on Germany's Ruhr Valley dams. Although the Lancaster was primarily a night bomber, it excelled in many other roles, including daylight precision bombing: in the latter role some Lancasters were adapted to carry the 12,000 lb Tallboy and, ultimately, the 22,000 lb Grand Slam earthquake bombs (also designed by Wallis).
As early as 1943, a Lancaster was converted to become an engine test bed for the Metropolitan-Vickers F.2 turbojet. Lancasters were later used to test several different engines, including the Armstrong Siddeley Mamba and Rolls-Royce Dart turboprops, and the Avro Canada Orenda and STAL Dovern turbojets. Postwar, the Lancaster was supplanted as the RAF's main strategic bomber by the Avro Lincoln, itself a larger permutation of the Lancaster. Instead the Lancaster took on the role of long range anti-submarine patrol aircraft (later supplanted by the Avro Shackleton) and air-sea rescue. It was also used in roles as diverse as photo-reconnaissance and aerial mapping, as a flying tanker for aerial refuelling, and as the Avro Lancastrian, a long-range, high-speed transatlantic passenger and postal delivery airliner. In March 1946, a Lancastrian of BSAA flew the first scheduled flight from the then new London Heathrow Airport.
The origins of the Lancaster stem from a twin-engined bomber design submitted to meet Air Ministry Specification P.13/36, which was for a new generation of twin-engined medium bombers for "worldwide use", the engine specified as the Rolls-Royce Vulture. The resulting aircraft was the Manchester, which, although a capable aircraft, was underpowered and troubled by the unreliability of the Vulture engine. Only 200 Manchesters were built, with the type withdrawn from service in 1942.
Avro's chief designer, Roy Chadwick, was already working on an improved Manchester design using four of the more reliable, but less powerful Rolls-Royce Merlin engines on a larger wing. The aircraft was initially designated Avro Type 683 Manchester III, and later renamed the "Lancaster". The prototype aircraft BT308 was assembled by Avro's experimental flight department at Manchester's Ringway Airport. Test pilot H.A. "Bill" Thorn took the controls for its first flight at Ringway, on Thursday, 9 January 1941. The aircraft proved to be a great improvement on its predecessor, being "one of the few warplanes in history to be 'right' from the start." Its initial three-finned tail layout, a result of the design being adapted from the Manchester I, was quickly changed on the second prototype DG595 and subsequent production aircraft, to the familiar twin-finned specification also used on the later Manchesters.
Some of the later orders for Manchesters were changed in favour of Lancasters; the designs were very similar and both featured the same distinctive greenhouse cockpit, turret nose, and twin tail. The Lancaster discarded the stubby central third tail fin of the early Manchesters and used the wider span tailplane and larger elliptical twin fins from the later Manchester IA.
The Lancaster is a mid-wing cantilever monoplane with an oval all-metal fuselage. The wing was constructed in five main sections, the fuselage in five sections. All wing and fuselage sections were built separately and fitted with all the required equipment before final assembly. The tail unit had twin elliptical fins and rudders. The Lancaster was initially powered by four wing-mounted Rolls-Royce Merlin piston engines driving 13ft diameter de Havilland Hydromatic three-bladed airscrews. It had retractable main landing gear and fixed tail-wheel, with the hydraulically operated main landing gear raising rearwards into the inner engine nacelles.
The majority of Lancasters built during the war years were manufactured by Avro at their factory at Chadderton near Oldham, Lancashire, and test flown from Woodford Aerodrome in Cheshire. Other Lancasters were built by Metropolitan-Vickers (1,080, also tested at Woodford), and Armstrong Whitworth. The aircraft was also produced at the Austin Motor Company works in Longbridge, Birmingham, later in the Second World War and postwar by Vickers-Armstrongs at Chester as well as at the Vickers Armstrong factory, Castle Bromwich, Birmingham. Only 300 of the Lancaster B II fitted with Bristol Hercules engines were constructed; this was a stopgap modification caused by a shortage of Merlin engines as fighter production was of higher priority. Many BIIs were lost after running out of fuel. The Lancaster B III had Packard Merlin engines but was otherwise identical to contemporary B Is, with 3,030 B IIIs built, almost all at Avro's Newton Heath factory. The B I and B III were built concurrently, and minor modifications were made to both marks as new batches were ordered. Examples of these modifications were the relocation of the pitot head from the nose to the side of the cockpit, and the change from de Havilland "needle blade" propellers to Hamilton Standard or Nash Kelvinator made "paddle blade" propellers.
Of later variants, only the Canadian-built Lancaster B X, manufactured by Victory Aircraft in Malton, Ontario, was produced in significant numbers. A total of 430 of this type were built, earlier examples differing little from their British-built predecessors, except for using Packard-built Merlin engines and American-style instrumentation and electrics. The final production version was the Mark VII and was made by the Austin motor company at their Longbridge factory. The main design difference with the Mark VII was the use of the American-built Martin dorsal gun turret in place of the English Nash & Thompson one; they had to be mounted slightly further forward on the fuselage for weight balance. All were produced too late for the war in Europe and were tropicalized and upgraded as the Mark VII (FE) for use in the Far East against Japan. A total of 7,377 Lancasters of all marks were built throughout the duration of the war, each at a 1943 cost of £45-50,000.
Starting at the nose, the bomb aimer had two positions to man. His primary location was lying prone on the floor of the nose of the aircraft, with access to the bombsight controls facing forward, with the bombsight computer on his left and bomb release selectors on the right. He also used his view out of the large transparent perspex nose cupola to assist the navigator with map reading. To man the Frazer Nash FN5 nose turret, he stood up placing himself in position behind the triggers of the twin .303 in (7.7 mm) guns. Ammunition for the turret was 1,000 rounds-per-gun (rpg) The bomb aimer's position contained the nose emergency hatch in the floor; at 22 inches by 26.5 inches (two inches narrower than the Halifax escape hatch) it was difficult to exit through while wearing a parachute. Compared with other contemporary aircraft, the Lancaster was not an easy aircraft to escape from; in a Halifax, 25% of downed aircrew bailed out successfully, and in American bombers (albeit in daylight raids) it was as high as a 50% success rate while only 15% of the Lancaster crew were able to bail out. Operational research experts (Freeman Dyson, amongst others) attempted unsuccessfully to have the escape hatch enlarged.
Moving back, on the roof of the bomb bay the pilot and flight engineer sat side by side under the expansive canopy, with the pilot sitting on the left on a raised portion of the floor (almost all British bombers, and most German bombers, had only a single pilot seat as opposed to American practice of carrying two pilots, or at least having controls for two pilots installed). The flight engineer sat on a collapsible seat (known as a "second dicky seat") to the pilot's right, with the fuel selectors and gauges on a panel behind him and to his right. The pilot and other crew members could use the panel above the cockpit as an auxiliary emergency exit while the mid-upper was expected to use the rear entrance door to leave the aircraft. The tail gunner escaped by rotating his turret to the side and dropping out backwards through the two rear turret doors.
Behind the pilot and flight engineer, and behind a curtain fitted to allow him to use light to work, sat the navigator. His position faced to port with a chart table in front of him. An instrument panel showing the airspeed, altitude, and other information required for navigation was mounted on the side of the fuselage above the chart table.
The wireless operator's radios were mounted on the left-hand end of the chart table, facing the rear of the aircraft. Behind these and facing forwards the wireless operator sat on a seat at the front of the main spar. On his left was a window, and above him was the astrodome, used for visual signalling and by the navigator for celestial navigation.
Behind the wireless operator were the two spars for the wing, which created a major obstacle for crew members moving down the fuselage even on the ground. On reaching the end of the bomb bay the floor dropped down to the bottom of the fuselage, and the mid-upper gunner's turret was reached. His position allowed a 360° view over the top of the aircraft, with two .303 in (7.7 mm) M1919 Browning machine guns to protect the aircraft from above and to the side. The mid-upper gunner had perhaps the most uncomfortable position of all the crew, as he was seated on a rectangle of canvas that was slung beneath the turret and would stay in position throughout the flight. Ammunition for the turret was 1,000 rounds-per-gun.
To the rear of the turret was the side crew door, on the starboard side of the fuselage. This was the main entrance to the aircraft, and also could be used as an emergency exit. Right at the tail-end of the fuselage, over the spars for the tailplane, and the Elsan chemical toilet, the rear gunner sat in his exposed position in the tail turret, which was entered through a small hatch in the rear of the fuselage. Depending on the size of the rear gunner, the area was so cramped that the gunner would often hang his parachute on a hook inside the fuselage, near the turret doors. Neither the mid-upper nor the rear gunner's position was heated, and the gunners had to wear electrically heated suits to prevent hypothermia and frostbite. Many rear gunners insisted on having the centre section of perspex removed from the turret to improve visibility. The transparencies were difficult to see through at night, particularly when trying to keep watch for enemy night fighters that appeared without notice astern and below the aircraft when getting into position to open fire. Ammunition for the tail turret was 2,500 rounds-per-gun, due to the weight the ammunition being stored in tanks situated near the mid-upper turret's position and fed rearward in runways down the back of the fuselage to the turret.
The Avro Lancaster was initially equipped with four Nash & Thomson Frazer Nash hydraulically operated turrets mounted in the nose, tail, mid-upper and underside. The original tail turret was equipped with four 0.303 inch (7.7 mm) Browning machine guns and all other turrets with two such machine guns.
Only the FN-5A nose turret which was similar to the FN-5 used on the preceding Avro Manchester, the Vickers Wellington and the Short Stirling remained unchanged during the life of the design, except in instances where it was removed entirely.
The ventral (underside) FN-64 turret quickly proved to be dead weight, being both difficult to sight because it relied on a periscope which limited the gunner's view to a 20 degree arc, and too slow to keep a target within its sights. Aside from early B Is and the prototype B IIs, the FN-64 was almost never used. When the Luftwaffe began using Schräge Musik to make attacks from below in the winter of 1943/1944, modifications were made, including downward observation blisters mounted behind the bomb aimer's blister and official and unofficial mounts for 50 in (12.7 mm) machine guns or even 20 mm cannon, firing through the ventral holes of the removed FN-64. The fitting of these guns was hampered as the same ventral position was used for mounting the H2S blister, which limited installations to those aircraft fitted with bulged bomb bays which interfered with the H2S.
The mid-upper (dorsal or top turret) was an FN-50 on early examples and the very similar FN-150 with improved sights and controls on later examples. On all but the earliest examples this turret was surrounded by a coaming which provided a track for a cam operated interruptor device which prevented the gunner from shooting the tail of his own aircraft. The Mk.VII and late Mk.X Lancasters used the heavier electrically-controlled Martin 250 CE 23A turret equipped with two 50 inch machine guns which was mounted further forward to preserve the aircraft's longitudinal balance, and because it had an internal mechanism to prevent firing on the aircraft itself, it did not require a coaming. Other experimental turrets were tried out, including the FN-79 and the Boulton-Paul Type H barbette system.
The tail turret was the most important defensive position and carried the heaviest armament. Despite this, the turrets used, starting with the FN-20, were never entirely satisfactory and numerous designs were tried. The FN-20 was replaced by the very similar FN-120 which used an improved gyroscopic gun sight (GGS). Gunners using both the FN-20 and 120 removed perspex and armour from the turret to improve visibility, but trials by the RAF showed that a Mosquito night fighter was still able to get within a very short distance of the tail gunner without being spotted, confirming what the Luftwaffe had already realised. The Rose turret attempted to improve on the FN turrets by being completely open to the rear (improving visibility and allowing easier emergency egress) and by being fitted with two .50 inch machine guns and was installed in a small number of Lancasters but never became common. The answer however was not better visibility - it was with radar. The FN-121 was the Automatic Gun Laying Turret (AGLT) - an FN-120 fitted with Village Inn gun-laying radar. Aircraft fitted with Village Inn were used as bait, flying behind the main formations to confront the night fighters that followed the formations and took down the stragglers. This significantly reduced operational losses and examples of the final turret used would also use gun laying radar. Prior to the end of the war, Lancasters built in the UK standardized on the FN-82 fitted with two .50 inch machine guns and fitted with gun-laying radar as production allowed, which was also used on early models of the Avro Lincoln. The downside with gun laying radar, and all radar and radio transmitting systems, is that attacking forces can pick up the transmissions and use them to vector onto the target.
Later in the war, Freeman Dyson made a case for removing all the Lancaster's defensive armament, arguing it would reduce the loss rate by increasing the Lancaster's speed by up to 50 mph (assuming the bomb load was not increased at the same time), and thus make it harder to shoot down. This became even more important when Dyson and Mike O'Loughlin concluded that some of the German night fighters were using Schräge Musik upward firing guns as the Lancaster had no ventral gun turret to defend itself, although any self-defence would have to be dependent on the crew realising they were being attacked from underneath. Dyson thought the modification would be worth it even if the loss rate was exactly the same as before on the grounds of saving the lives of the two air gunners from each downed plane. The case for speed over defensive armament was supported by the de Havilland Mosquito whose loss rates were far lower than the Lancaster's. As an example, during the Battle of Berlin (18 November 1943 to 30 March 1944) the average loss rate of the heavy bombers (overwhelmingly Lancasters) was 5.1%, whereas for Mosquitoes it was 0.5%, though since a speed optimised Lancaster would still be up to 50 mph slower than a Mosquito it wouldn`t have been expected to equal the latter aircraft`s loss rates.
An important feature of the Lancaster was its unobstructed, 33 ft long, bomb bay. At first, the heaviest bomb carried was the 4,000 lb high capacity HC "Cookie". Bulged doors were added to 30% of B Is to allow the aircraft to carry 8,000 lb and later 12,000 lb "Cookies". The Lancaster also carried a variety of smaller weapons, including the Small Bomb Container (SBC) which held 236 4 lb or 24 30 lb incendiary and explosive incendiary bomblets; 500 lb and 1,000 lb General Purpose High Explosive (GP/HE) bombs (these came in a variety of designs); 1,850 lb parachute deployed magnetic or acoustic mines, or 2,000 lb armour piercing (AP) bombs; 250 lb Semi-Armour-Piercing (SAP) bombs, used up to 1942 against submarines; post 1942: 250 lb or 500 lb anti-submarine depth charges.
In 1943 617 Squadron was created to carry out Operation Chastise, the raid against the Ruhr dams. This unit was equipped with B.III (Specials), officially designated the "Type 464 (Provisioning)", modified to carry the 9,250 pound (4,196 kg) "Upkeep" bouncing bomb (which was referred to as a mine). The bomb bay doors were removed and the ends of the bomb bay were covered with fairings. "Upkeep" was suspended on pivoted, vee-shaped struts which sprang apart when the bomb-release button was pressed. A drive belt and pulley to rotate the bomb at 500 rpm was mounted on the starboard strut and driven by a hydraulic motor housed in the forward fairing. The mid-upper turret was removed and a more bulbous bomb aimer's blister was fitted; this, as "Mod. 780", later becoming standard on all Lancasters, while the bombsight was replaced by a simple aiming device. Two Aldis lights were fitted in the rear bomb bay fairing; the optimum height for dropping "Upkeep" was 60 ft and, when shone on the relatively smooth waters of the dam's reservoirs, the light beams converged into a single spot when the Lancaster was flying at the correct height.
Towards the end of the war, attacking special and hardened targets, other variants of B I Specials were modified to carry the 21 ft long 12,000 lb "Tallboy" or 25.5 ft long 22,000 lb "Grand Slam" "earthquake" bombs: to carry the "Grand Slam" extensive modifications to the aircraft were required. The modifications included removal of the mid-upper turret and the removal of two guns from the rear turret; removal of the cockpit armour plating (the pilot's seatback) and installation of Rolls-Royce Merlin Mk 24 Engines which had better take-off performance. The bomb bay doors were removed and the rear end of the bomb bay cut away to clear the tail of the bomb. Later the nose turret was also removed to further improve performance. The undercarriage was strengthened and stronger mainwheels, later used by the Avro Lincoln, were fitted.
There were 7,377 produced