A | B | C | D | E | F | G | H | CH | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
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| Lancaster B.I PA474[note 1] of the RAF Battle of Britain Memorial Flight in 460 Squadron (RAAF) colours | |
| Role | Heavy bomber |
| National origin | United Kingdom |
| Manufacturer | Avro |
| Designer | Roy Chadwick |
| Built by | Avro and five others (in UK & Canada) |
| First flight | 9 January 1941 |
| Introduction | February 1942 |
| Retired | April 1, 1964 Royal Canadian Air Force |
| Primary users | Royal Air Force Royal Canadian Air Force Royal Australian Air Force |
| Number built | 7,377[1] |
| Developed from | Avro Manchester |
| Variants | Avro Lancastrian |
| Developed into | Avro York Avro Lincoln |
The Avro Lancaster is a British Second World War heavy bomber. It was designed and manufactured by Avro as a contemporary of the Handley Page Halifax, both bombers having been developed to the same specification, as well as the Short Stirling, all three aircraft being four-engined heavy bombers adopted by the Royal Air Force (RAF) during the same era.
The Lancaster has its origins in the twin-engine Avro Manchester which had been developed during the late 1930s in response to the Air Ministry Specification P.13/36 for a medium bomber for "world-wide use" which could carry a torpedo internally, and make shallow dive-bombing attacks. Originally developed as an evolution of the Manchester (which had proved troublesome in service and was retired in 1942), the Lancaster was designed by Roy Chadwick and powered by four Rolls-Royce Merlins and in one of the versions, Bristol Hercules engines. It first saw service with RAF Bomber Command in 1942 and as the strategic bombing offensive over Europe gathered momentum, it was the main aircraft for the night-time bombing campaigns that followed. As increasing numbers of the type were produced, it became the principal heavy bomber used by the RAF, the Royal Canadian Air Force (RCAF) and squadrons from other Commonwealth and European countries serving within the RAF, overshadowing the Halifax and Stirling, two other commonly used bombers.[2]
A long, unobstructed bomb bay meant that the Lancaster could take the largest bombs used by the RAF, including the 4,000 lb (1,800 kg), 8,000 lb (3,600 kg) and 12,000 lb (5,400 kg) "blockbusters", loads often supplemented with smaller bombs or incendiaries. The "Lanc", as it was known colloquially,[3] became one of the most heavily used of the Second World War night bombers, delivering 608,612 long tons (618,378,000 kg) of bombs in 156,000 sorties.[4] The versatility of the Lancaster was such that it was chosen to equip 617 Squadron and was modified to carry the Upkeep "bouncing bomb" designed by Barnes Wallis for Operation Chastise, the attack on German Ruhr valley dams. Although the Lancaster was primarily a night bomber, it excelled in many other roles, including daylight precision bombing, for which some Lancasters were adapted to carry the 12,000 lb (5,400 kg) Tallboy and then the 22,000 lb (10,000 kg) Grand Slam earthquake bombs (also designed by Wallis).[5] This was the largest payload of any bomber in the war.
In 1943, a Lancaster was converted to become an engine test bed for the Metropolitan-Vickers F.2 turbojet. Lancasters were later used to test other 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 main strategic bomber of the RAF by the Avro Lincoln, a larger version of the Lancaster. 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 for 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 new London Heathrow Airport.[6]
Development
Origins
In the 1930s, the Royal Air Force (RAF) was primarily interested in twin-engine bombers.[7] These designs put limited demands on engine production and maintenance, both of which were already stretched with the introduction of so many new types into service. Power limitations were so serious that the British invested heavily in the development of huge engines in the 2,000 hp (1,500 kW) class in order to improve performance. During the late 1930s, none of these were ready for production. Both the United States and the Soviet Union were pursuing the development of bombers powered by arrangements of four smaller engines; the results of these projects proved to possess favourable characteristics such as excellent range and fair lifting capacity. Accordingly, in 1936, the RAF also decided to investigate the feasibility of the four-engined bomber.[7]
The origins of the Lancaster stem from a twin-engined bomber that had been submitted to British Air Ministry Specification P.13/36 of 1936 for a twin-engined medium bomber for "worldwide use" which could carry a torpedo internally, and make shallow dive-bombing attacks.[8][9] Further requirements of the specification included the use of a mid-mounted cantilever monoplane wing, and all-metal construction while the use of the Rolls-Royce Vulture, which was in development was encouraged.[10] Twin-engine designs were submitted by Fairey, Boulton Paul, Handley Page and Shorts, using Rolls-Royce Vulture, Napier Sabre, Fairey P.24 or Bristol Hercules engines. Most of these engines were still under development and while four-engined bomber designs were considered for specification B.12/36 for a heavy bomber, the extra engines required the wing and overall aircraft structure to be stronger, increasing the structural weight.[11]
Avro submitted the Avro 679 to fulfil Specification P.13/36 and, in February 1937, Avro's submission was selected, along with Handley Page's bid as a backup. In April 1937, a pair of prototypes for each design was ordered.[12][10] Avro's aircraft, named the Manchester, entered RAF service in November 1940. Although a capable aircraft, the Manchester was underpowered and its Vulture engines proved to be unreliable.[13][14] As a result, only 200 were constructed and the type was withdrawn from service in 1942.[15]
Flight testing
By mid-1940, Avro's chief design engineer, Roy Chadwick, was working on an improved Manchester[13] powered by four of the more reliable but less powerful Rolls-Royce Merlin engines, specifically adopting the "Power-egg" installation developed for the Beaufighter II, and installed on a wing of increased span.[16] Initially, the improved aircraft was designated as the Type 683 Manchester III but was subsequently renamed the Lancaster. The prototype, serial number BT308, was assembled by the Avro experimental flight department at Ringway Airport, Manchester, being modified from a production Manchester airframe, combined with the new wing to accommodate the additional engines.[13] The first flight was made by test pilot H. A. "Sam" Brown on 9 January 1941 at RAF Ringway, Cheshire.[17]
Flight testing of the new aircraft quickly proved it to be a substantial improvement over its predecessor.[18] The first prototype was initially outfitted with the Manchester I's three-finned tail but this was revised on the second prototype, DG595, and subsequent production Lancasters used the larger elliptical twin-finned tail unit that was also adopted for the last Manchesters built.[13] This not only increased stability but also improved the dorsal gun turret's field of fire. The second prototype was also fitted with more powerful Merlin XX engines.[13]
Manchesters still on the production line were converted into Lancaster B.Is.[13][17] Based upon its performance, a decision was taken early on to reequip twin-engine bomber squadrons with the Lancaster as quickly as possible.[13] L7527, The first production Lancaster made its first flight in October 1941, powered by Merlin XX engines.[13][17]
Production
Avro received an initial contract for 1,070 Lancasters.[13] The majority of Lancasters manufactured during the war years were constructed by Avro at its factory at Chadderton near Oldham, Lancashire and were test-flown from Woodford Aerodrome in Cheshire. As it was quickly recognised that Avro's capacity was exceeded by the wartime demand for the type, it was decided to form the Lancaster Aircraft Group, which comprised a number of companies that undertook the type's manufacture, either performing primary assembly themselves or producing various subsections and components for the other participating manufacturers.[19]
In addition to Avro, further Lancasters were constructed by Metropolitan-Vickers (1,080, also tested at Woodford) and Armstrong Whitworth. They were also produced at the Austin Motor Company works in Longbridge, Birmingham, later in the Second World War and post-war by Vickers-Armstrongs at Chester as well as at the Vickers Armstrong factory, Castle Bromwich, Birmingham. Belfast-based aircraft firm Short Brothers had also received an order for 200 Lancaster B.Is, but this was cancelled before any aircraft had been completed.[20][21]
The Lancaster was also produced overseas. During early 1942, it was decided that the bomber should be produced in Canada, where it was manufactured by Victory Aircraft in Malton, Ontario.[22] Of later variants, only the Canadian-built Lancaster B X 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 instruments and electrics.[citation needed] In August 1942, a British-built Lancaster B.I was dispatched to Canada as a pattern aircraft, becoming the first of the type to conduct a transatlantic crossing.[22] The first Lancaster produced in Canada was named the "Ruhr Express".[note 2][citation needed] The first batch of Canadian Lancasters delivered to England suffered from faulty ailerons; this error was subsequently traced to the use of unskilled labour.[23] By the end of the conflict, over 10,000 Canadians were employed on the production line, which was producing one Lancaster each day.[24]
Factories
| Manufacturer | Location | Coordinates | Number produced |
|---|---|---|---|
| A. V. Roe | Woodford | 53°20′28″N 2°09′25″W / 53.341173°N 2.156986°W | 2,978 |
| Chadderton | 53°31′49″N 2°10′29″W / 53.530139°N 2.174784°W | ||
| Yeadon | 53°52′29″N 1°39′36″W / 53.874647°N 1.660124°W | 695 | |
| Armstrong Whitworth | Whitley | 52°22′59″N 1°29′26″W / 52.382954°N 1.490615°W | 1,329 |
| Austin Motors | Longbridge | 52°23′00″N 1°59′12″W / 52.383362°N 1.986706°W | 330 |
| Marston Green | 52°27′25″N 1°43′52″W / 52.456983°N 1.730976°W | ||
| Metropolitan-Vickers | Trafford Park | 53°27′51″N 2°19′07″W / 53.464243°N 2.318726°W | 1,080 |
| Vickers-Armstrongs | Castle Bromwich | 52°30′59″N 1°48′33″W / 52.516301°N 1.809229°W | 300 |
| Chester | 53°10′25″N 2°58′37″W / 53.173551°N 2.977013°W | 235 | |
| Victory Aircraft | Malton (Canada) | 43°42′04″N 79°38′31″W / 43.701047°N 79.642023°W | 430 |
Further development
The Lancaster B.I was never fully superseded in production by a successor model, remaining in production until February 1946.[20] According to aviation authors Brian Goulding and M. Garbett, the Lancaster B.I altered little during its production life, partially as a result of the sound basic structure and design; of the visible changes, the fuselage side windows were deleted, the Perspex chin of the bomb-aimer was enlarged, and a larger astrodome was provided.[25] Various additional bumps and blisters were also added, which typically housed radar equipment and radio navigational aids. Some Lancaster B.I bombers were outfitted with bulged bomb bay doors in order to accommodate increased armament payloads.[25]
Early production Lancaster B.Is were outfitted with a ventral gun turret position.[22] In response to feedback on the lack of application for the ventral turret, the ventral turret was often eliminated during the course of each aircraft's career. While some groups chose to discard the position entirely, various trials and experiments were performed at RAF Duxford, Cambridgeshire and by individual squadrons.[22] A total of 50 Austin-built Lancaster B.Is was constructed to a non-standard configuration, having a Frazer Nash turret installed directly above the bomb bay; however, this modification was largely unpopular due to its obstruction of the internal walkway, hindering crew movements. Various other turret configurations were adopted by individual squadrons, which included the removal of various combinations of turrets.[26]
The Lancaster B.III was powered by Packard Merlin engines, which had been built overseas in the United States, but was otherwise identical to contemporary B.Is.[20] In total, 3,030 B.IIIs were constructed, almost all of them at Avro's Newton Heath factory. The Lancaster B.I and B.III were manufactured concurrently and minor modifications were made to both marks as further batches were ordered. The B.I and B.III designations were effectively interchangeable simply by changing the engines used, which was occasionally done in practice.[20] Examples of modifications made include 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.[27]
Design
Overview
The Avro Lancaster was a British four-engined strategic bomber that was used as the RAF's principal heavy bomber during the latter half of the Second World War. The typical aircraft was powered by an arrangement of four wing-mounted Rolls-Royce Merlin piston engines, each of which drove a 13 ft (4.0 m) diameter de Havilland Hydromatic three-bladed propeller. While not optimal, the Lancaster was capable of flying the return journey home on only two operational engines, along with very limited distances on a single running engine.[20] Aviation authors Brian Goulding and M. Garbett have claimed that experienced Lancaster pilots were often able to out-manoeuver Luftwaffe fighters.[28] It possessed largely favourable flying characteristics, having been described by Goulding and Garbett as being: "a near-perfect flying machine, fast for its size and very smooth...such a delightfully easy aeroplane to fly...there are instances of Lancasters having been looped and barrel-rolled, both intentionally and otherwise".[28]
The Lancaster benefited from a structure that possessed considerable strength and durability, which had been intentionally designed to maximise structural strength-per-weight; this resulted in the Lancaster being capable of withstanding some levels of damage resulting from attacks by hostile interceptor aircraft and ground-based anti-aircraft batteries.[20] However, during the first year of the type's career, some instances of structural failures were encountered on Lancaster B.Is and a number of aircraft were lost in accidents as a result of the design limitations having been greatly exceeded.[28] Compared with other contemporary aircraft, the Lancaster was not an easy aircraft to escape from as its escape hatch was only 22 in × 26.5 in (56 cm × 67 cm) in size; in a Halifax or Stirling (which both had an escape hatch 2 in (5.1 cm) wider), 25 per cent of downed aircrew bailed out successfully, and in American bombers (albeit in daylight raids) it was as high as a 50 per cent success rate while only 15 per cent of the Lancaster crew were able to bail out.[29]
The Lancaster uses a mid-wing cantilever monoplane configuration. The wing is constructed from five separate main sections while the fuselage is likewise composed of five sections. Aside from a few elements, such as the fabric-covered ailerons, the Lancaster's oval-shaped fuselage had an all-metal covering.[22] All of the wing and fuselage sections were manufactured separately, during which they were outfitted with all of the required equipment in advance of final assembly being performed, as a measure intended to accelerate the rate of production. The Lancaster was equipped with a retractable main undercarriage and fixed tailwheel; the hydraulically-actuated main landing gear raised rearwards into recesses within the inner engine nacelles.[30] The distinctive tail unit of the aircraft was outfitted with a large twin elliptical fins and rudder arrangement.[28]
Like any aeroplane, the Lancaster was not viceless in its handling. In a dive, it had a tendency to go more deeply into the dive as speed increased. Not all aeroplanes did this, for example, the Halifax tended to get increasingly tail-heavy as speed increased, and thus fly itself out of the dive.[31] Furthermore, the Lancaster suffered longitudinal instability at speeds above 200 mph (320 km/h).[32]
Crew accommodation
The standard crew for a Lancaster consisted of seven men, stationed in various positions in the fuselage. 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 Mark XIV bomb sight on his left and bomb release selectors on the right. He also used his view through the large transparent perspex nose cupola to assist the navigator with map reading.[citation needed] 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 by 26.5 inches (560 by 670 mm) (two inches narrower than the Halifax escape hatch) it was difficult to exit through while wearing a parachute. Operational research experts, including British scientist Freeman Dyson, amongst others, attempted unsuccessfully to have the escape hatch enlarged.[citation needed]
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 the 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 gunner was expected to use the rear entrance door to leave the aircraft. The tail gunner escaped by rotating his turret to the rear, opening the door in the back of the turret, passing into the fuselage, and clipping on a parachute that was hung on the side wall. He could then exit through the rear entrance door.[33]
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.[34]
Behind the wireless operator were the two spars of the wing, which created a major obstacle for crew members moving down the fuselage even on the ground. At the end of the bomb bay was the mid-upper gunner's turret, at which the floor dropped down to the fuselage's bottom. His position allowed a 360° view over the top of the aircraft, with two Browning .303 Mark IIs to protect the aircraft from above and to the side. The mid-upper gunner sat on a rectangle of canvas that was slung beneath the turret and would stay in position throughout the flight. The turret had 1,000 rounds of ammunition per gun.[citation needed]
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. The Elsan chemical toilet, a type of aircraft lavatory, was located near the spars for the tailplane. At the extreme tail-end of the fuselage, 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.[citation needed]
Armament
Defensive armament
The Avro Lancaster was initially equipped with four Nash & Thompson Frazer Nash hydraulically operated turrets mounted in the nose, tail, mid-upper and underside. The original tail turret was equipped with four Browning .303 Mark II machine guns and all other turrets with two such machine guns.[35][36][37]
Late on in the war, Freeman Dyson (as a 19-year-old who had yet to win a degree) put forward a case for the removal of the majority of the Lancaster's defensive armament. He argued that this would reduce the loss rate by increasing the Lancaster's cruising speed by up to 50 mph (80 km/h) (assuming the bomb load was not increased), making the bomber harder to intercept.[38] He also claimed reducing defensive air gunners would reduce human losses incurred with each aircraft lost.[39] However this neglects the fact that the two main Luftwaffe night fighters of the time, the Messerschmitt Bf 110 and the Junkers Ju 88 night fighters were capable of over 300 mph (480 km/h), thus a 50 mph (80 km/h) increase over the Lancaster's normal cruising speed of around 180 mph (290 km/h), giving a speed of 230 mph (370 km/h), still left the Lancaster vulnerable to interception. The introduction of the Heinkel He 219 and Messerschmitt Me 262 night fighters erased any speed advantage and would have left the aircraft undefended. Consequently, Dyson's proposal was not adopted.
Nose turret
Only the FN-5A[35] 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.
Ventral turret
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,[35] and too slow to keep a target within its sights.[note 3] 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[40] and official[41] and unofficial mounts for .50 in (12.7 mm) machine guns or even 20 mm (0.79 in) 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.[35]
Mid-upper turret
The mid-upper (dorsal or top) turret was an FN-50[35][36] on early examples and the very similar FN-150 with improved sights and controls[35] on later examples. On all but the earliest examples, this turret was surrounded by a coaming which provided a track for a cam-operated interrupter device which prevented the gunner from shooting the tail of his own aircraft.[35] The Mk.VII and late Mk.X Lancasters used the heavier, electrically controlled Martin 250 CE 23A turret equipped with two .50 in (13 mm) machine guns[35] 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.[note 4][35] Other experimental turrets were tried out, including the FN-79 and the Boulton-Paul Type H barbette system.[35]
Tail turret
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).[35] 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. This removal of perspex from the turret was called the "Gransden Lodge" modification. Ammunition for the tail turret was 2,500 rounds per gun. Due to the weight, the ammunition was 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.[42]
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 in (13 mm) machine guns. It was installed in a small number of Lancasters but never became common.[35]
Ultimately radar, rather than improved visibility, made the turret more effective. The FN-121 was the Automatic Gun Laying Turret (AGLT), an FN-120 fitted with Village Inn gun-laying radar.[35] Aircraft fitted with Village Inn were used as bait, flying behind the main formations to confront the night fighters that followed the formations and shot down stragglers. This significantly reduced operational losses; and gun-laying radar was added to the last versions of the turret. Before the end of the war Lancasters built in the UK standardised on the FN-82 fitted with two .50 in (13 mm) machine guns and a gun-laying radar as production allowed, which was also used on early models of the Avro Lincoln. The disadvantage of all radar and radio transmitting systems is that attacking forces can locate aircraft by picking up transmissions.[citation needed]
Bombs
An important feature of the Lancaster was its unobstructed 33 ft (10 m) long bomb bay. At first, the heaviest bomb carried was the 4,000 lb (1,800 kg) high capacity HC "Cookie".[44] Bulged doors were added to 30 per cent of B.Is to allow the aircraft to carry 8,000 lb (3,600 kg) and later 12,000 lb (5,400 kg) "Cookies". The Lancaster also carried a variety of smaller weapons, including the Small Bomb Container (SBC) which held 236 4 lb (1.8 kg) or 24 30 lb (14 kg) incendiary and explosive incendiary bomblets; 500 lb (230 kg) and 1,000 lb (450 kg) General Purpose High Explosive (GP/HE) bombs (these came in a variety of designs); 1,850 lb (840 kg) parachute deployed magnetic or acoustic mines, or 2,000 lb (910 kg) armour-piercing (AP) bombs; 250 lb (110 kg) Semi-Armour-Piercing (SAP) bombs, used up to 1942 against submarines; post-1942: 250 lb (110 kg) or 500 lb (230 kg) anti-submarine depth charges.[citation needed]
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 lb (4,200 kg) "Upkeep" bouncing bomb.[45][note 5] The bomb bay doors were removed and the ends of the bomb bay were covered with fairings. "Upkeep" was suspended on laterally pivoted, vee-shaped struts which sprang apart beamwise 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 became standard on all Lancasters, while the bombsight was replaced by a simple aiming device that consisted of a simple triangle of wood with a peephole at one corner and a nail in each of the other corners such that at the correct distance the nails coincided with the towers on the dams. Because each dam was a different width between the towers, each plane carried two or three different sights.[46][47] Two Aldis lights were fitted in the rear bomb bay fairing, aimed forward so the bomb aimer could see the converging lights below his blister in the nose; the optimum height for dropping "Upkeep" was 60 ft (18 m) and, when shone on the relatively smooth waters of the dam's reservoirs, the light beams converged into a figure 8 when the Lancaster was flying at the correct height.[46][48] The Type 464 Lancaster was also fitted with VHF radios (normally reserved for fighters) so that Gibson, the squadron leader, could control the operation while over the target,[49] an early example of what became the master bomber role.
After the 'Dam Busters' raid 617 Squadron was converted to a high-altitude precision bombing squadron in preparation for the arrival of Barnes Wallis's forthcoming Earthquake bombs for attacking special and hardened targets, and while they were training for this the bouncing bomb variants of B.I Specials had the spars and equipment removed and were then modified to carry the 21 ft (6.4 m) long 12,000 lb (5,400 kg) "Tallboy" bomb, a scaled-down version of the upcoming 25.5 ft (7.8 m) long 22,000 lb (10,000 kg) "Grand Slam" "earthquake" bombs which were still being built. Aircraft intended to carry the "Grand Slam" required extensive modifications. These included the removal of the dorsal turret and of two guns from the rear turret, the removal of the cockpit armour plating (the pilot's seatback), and the installation of Rolls-Royce Merlin Mk 24 engines for 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. A strengthened undercarriage and stronger mainwheels, later used by the Avro Lincoln, were fitted.[5][note 6]
Specific bomb loads were standardised and given code names by Bomber Command:[50]
| Codename | Type of raid or target | Bomb load |
|---|---|---|
| "Arson" | incendiary area bombing | 14 SBC, each with 236 x 4 lb (1.8 kg) Incendiary and Explosive Incendiary bomblets, total 3,304. |
| "Abnormal" | factories, railway yards, dockyards | 14 x 1,000 lb (450 kg) GP/HE bombs using both impact and long delay (up to 144 hours) fuses. |
| "Cookie"—or—"Plumduff" | Blast, demolition and fire | 1 x 4,000 lb (1,800 kg) impact-fused HC bomb. 3 x 1,000 lb (450 kg) GP/HE bombs, and up to 6 SBCs with 1,416 incendiary bomblets. |
| "Gardening" | Mining of ports, canals, rivers and seaways | 6 x 1,850 lb (840 kg) parachute mines. |
| "No-Ball" | V-1 flying bomb launch sites | 1 x 4,000 lb (1,800 kg) impact fused HC and up to 18 x 500 lb (230 kg) GP bombs, with both impact and delay fusing. |
| "Piece" | Docks, fortifications and ships | 6 x 2,000 lb (910 kg) short-delay fused AP bombs, plus other GP/HE bombs based on local needs or availability. |
| "Plumduff-Plus" | Heavy industry | 1 x 8,000 lb (3,600 kg) impact or barometric fused HC and up to 6 x 500 lb (230 kg) impact or delay fused GP/HE bombs. |
| "Usual" | Blast and incendiary area bombing | 1 x 4,000 lb (1,800 kg) impact-fused HC bomb, and 12 SBCs with a total of 2,832 incendiary bomblets. |
| no code name given | Medium-range low altitude tactical raids | 6 x 1,000 lb (450 kg) short and long delay fused GP/HE bombs, additional 250 lb (110 kg) GP/HE bombs sometimes added. |
| no code name given | Submarines | (up to 1942): 5 x 250 lb (110 kg) short-delay fuse SAP bombs for surfaced U-boats; (post-1942): 6 x 500 lb (230 kg) and 3 x 250 lb (110 kg) anti-submarine depth charge bombs. |
