No one would dispute the statement that the Avro 683 Lancaster was the finest British heavy bomber of World War II. A few would even argue that it was the finest heavy bomber serving on any side during the conflict, and it is therefore strange to recall that it had its genesis in the unsuccessful twin-engined Avro 679 Manchester.

However, it is not entirely true to say that the Lancaster was virtually a four-engined Manchester; a four-engined installation in the basic airframe had been proposed before Manchester deliveries to the RAF began. But the prototype Lancaster was, in fact, a converted Manchester airframe with an enlarged wing centre section and four 1,145 hp (854 kW) Rolls-Royce Merlin Xs. This prototype initially retained the Manchester's triple tail assembly but was later modified to the twin fin and rudder assembly which became standard on production Lancasters.

The BT308 prototype flew on 9 January 1941 and later that month went to the Aircraft and Armament Experimental Establishment, Boscombe Down, to begin intensive flying trials. The second prototype DG595, with some modifications and Merlin XX engines rated at 1,280 hp (955 kW) for take-off , flew on 13 May 1941. In September of the same year the first prototype and several Manchester pilots were transferred to No.44 (Rhodesia) Squadron at Waddington for crew training and evaluation. The first three production aircraft were not delivered to the unit until Christmas Eve with another four aircraft arriving on December 28. No. 97 Squadron was the next unit to get the Lancaster in January 1942 followed by No. 207 Squadron in March 1942. The new bomber was an immediate success, and large production orders were placed. Such was the speed of development in wartime that the first production Lancaster was flown in October 1941, a number of partially completed Manchester airframes being converted on the line to emerge as Lancaster Is (from 1942 redesignated Lancaster B.Mk Is).

Avro's first contract was for 1,070 Lancasters, but others soon followed, and when it became obvious that the parent company's Chadderton and Yeadon production facilities would be unable to cope with the demand, other companies took on the task of building complete aircraft. They included Armstrong Whitworth at Coventry, Austin Motors at Birmingham, Metropolitan Vickers at Manchester and Vickers Armstrong at Chester and Castle Bromwich. Additionally, a large number of sub-contractors were involved in various parts of the country.

Lancasters soon began to replace Manchesters, and such was the impetus of production that a shortage of Merlin engines was threatened. This was countered by licence-production by Packard in the USA of the Merlin engine not only for Lancasters but also for other types.

An additional insurance was effected in another way, by the use of Bristol Hercules VI or XVI 14-cylinder sleeve-valve radial engines driving Rotal airscrews which in contrast to the Merlin airscrews, rotated counter-clockwise. Both engines were rated at 1,615 hp (1205 kW) for take-off. In this form, known as the Lancaster B.Mk II, prototype BT310 was flown on 26 November 1941 and results were sufficiently encouraging to warrant this version going into production by Armstrong Whitworth at Coventry. Delays were caused by the Ministry of Aircraft Production's insistence on maintaining construction of Whitley bombers, but in May 1942 the changeover to Lancaster B.II production began, only to be halted for four months as a result of air-raid damage.

A Canadian built (Victory Aircraft) Avro 683 Lancaster B.Mk X

The first two Hercules-powered Lancasters were completed in September 1942 and went to the Aircraft and Armament Experimental Establishment, where they were later joined by the third. Other Mk lIs from this first production batch were delivered to No. 61 Squadron at Syerston, Nottingham, the service trials unit for this version and a former Lancaster B.Mk I squadron. Early use of the Lancaster B.Mk II by No. 61 Squadron was plagued with minor problems, but during its six months of operations the squadron did not lose a single B.Mk II aircraft and in February 1943 was able to hand over the full complement of nine aircraft to No. 115 Squadron at East Wretham, a Wellington unit in No.3 Group.

Gradually Lancaster B.Mk IIs began to re-equip other squadrons, but the B.Mk II was never to achieve the success of the Merlin-engined Lancasters. It could not attain so high an altitude, was slightly slower, and had a bomb load 4,000 lbs (1814 kg) less than the other marks. Production ceased after 301 had been built, and the Armstrong Whitworth factory changed over to Lancaster B.Mk ls. It has been said that the phasing out of the Lancaster B.Mk II was in order to effect standardization, for the Handley Page Halifax B.III with Hercules engines was able to offer equal if not better possibilities, and with Lancaster B.Mk Is, Short Stirling's and Halifax’s all in service, variations in spares requirements needed to be cut as much as possible.

The final Lancaster B.Mk II operation was flown by No. 514 Squadron on 23 September 1944, but a few continued in service for a short while into the postwar era, mainly as test-beds, until the last survivor was scrapped in 1950. Although overshadowed by its Merlin-engined contemporaries, the Lancaster B.Mk II did not disgrace itself and achieved on average more than 150 flying hours per aircraft.

Meanwhile, the Merlin Lancasters were going from strength to strength. The prototype's engines gave way to 1,280 hp (954 kW) Merlin XXs and XXlIs, or 1,620 hp (1209 kW) for take-off Merlin XXIVs in production aircraft. Early thoughts of fitting a ventral turret were soon discarded, and the Lancaster B.Mk I had three Frazer-Nash hydraulically operated turrets with eight 0.303 in (7.7 mm) Browning machine-guns: two each in the nose and mid-upper dorsal positions and four in the tail turret. The bomb-bay, designed originally to carry 4,000 lbs (1814 kg) of bombs, was enlarged progressively to carry bigger and bigger bombs: up to 8,000 and 12,000 lbs (3629 and 5443 kg) and eventually to the enormous 22,000 lbs (9979 kg) 'Grand Slam', the heaviest bomb carried by any aircraft in World War II.

Production of the Lancaster was a comparatively simple affair considering its size. It had been designed for ease of construction and this undoubtedly contributed to the high rate of production. Lancasters were built to the total of 7,377 all marks. As mentioned earlier, No. 44 Squadron was the first to receive a Lancaster when the prototype arrived for trials and this squadron was also the first to be fully equipped with Lancasters, notching up another 'first' when it used the type operationally on 3 March 1942 to lay mines in "Operation Gardening" against Heligoland Bight on the German coast.

The Lancaster's existence was not revealed to the public until 17 April of that year, when 12 aircraft from Nos. 44 and 97 Squadrons carried out an unescorted daylight raid on Augsburg, near Munich. Flown at low level, the raid inflicted considerable damage on the MAN factory producing U-boat diesel engines, but the cost was high, seven aircraft being lost. Squadron Leaders Nettleton and Sherwood each received the Victoria Cross, the latter posthumously, for leading the operation which perhaps confirmed to the Air Staff that unescorted daylight raids by heavy bombers were not a practicable proposition and it was to be more than two years before the US Army Air Force was to resume such attacks.

As Packard-built Merlins became available, so the Lancaster B.Mk III appeared with these engines, although the B.Mk I remained in production alongside the Packard-engined B.Mk III. Externally the B.Mk III was distinguishable by an enlarged bomb aimer's 'bubble' in the nose but there were few other differences other than in minor equipment changes.

To swell the UK production lines, Victory Aircraft in Canada was chosen in 1942 to build Lancasters, and these were known as B.Mk Xs. Powered by Packard-built Merlins, the Canadian Lancasters were delivered by air across the Atlantic and had their armament fitted on arrival in the UK. The first B.Mk X was handed over on 6 August 1943, and 430 were built before production was completed.

Mention must be made of the Lancaster B.Mk VI, production of which was proposed using Merlin 85 or 87 engines, of 1,635 hp (1219 kW). Nine airframes were converted by Rolls Royce for comparative tests. No. 635 Squadron used several operationally on pathfinder work with nose and dorsal turrets removed. and fitted with improved H2S radar bombing aid and early electronic countermeasure equipment, but although performance was superior to the earlier marks no production aircraft were built.

It would be true to say that development of the Lancaster went hand-in-hand with development of bombs. The early Lancasters carried their bomb loads in normal flush-fitting bomb bays, but as bombs got larger it became necessary, in order to be able to close the bomb doors, to make the bays deeper so that they protruded slightly below the fuselage line. Eventually, with other developments, the bomb doors were omitted altogether for certain specialist types of bomb.

In this connection the most drastic changes suffered by the Lancaster were made to enable Dr Barnes Wallis's 'bouncing bombs' to be carried to the Ruhr by No. 617 Squadron in its attacks on the Mohne, Ederand Sorpe dams, probably the best known raid made by either side in the European theatre during World War II. For this operation, the Lancaster B.Mk IIIs had their bomb doors and front turrets removed and spotlights fitted beneath the wings arranged in such a way that the beams merged at exactly 60 feet (18.3 m) below the aircraft, the altitude from which the bombs had to be dropped if they were to be effective. Nineteen Lancasters took part in the attack on the night of 17 May 1943, the attackers breaching the Mohne and Eder dams for the loss of eight aircraft.

The German battleship Tirpitz was attacked on several occasions by Lancasters until, on 12 November 1944, a combined force from Nos. 9 and 617 Squadrons found the battleship in Tromso Fjord, Norway, and sank her with the 12,000 lbs (5443 kg) 'Tallboy' bombs, also designed by Barnes Wallis. The ultimate in conventional high explosive bombs was reached with the 22,000 lbs (9979 kg) 'Grand Slam', a weapon designed to penetrate concrete and explode some distance beneath the surface, so creating an earthquake effect. No. 617 Squadron first used the 'Grand Slam' operationally against the Bielefeld Viaduct on 14 March 1945, causing considerable destruction amongst its spans.

Final production version of the Lancaster was the B.Mk VII, which had an American Martin dorsal turret with two 0.50 in (12.7 mm) machine-guns in place of the normal Frazer-Nash turret. The new turret was also located further forward.

In spite of the other variants built from time to time, the Lancaster B.Mk I (B.Mk 1 from 1945) remained in production throughout the war, and the last was delivered by Armstrong Whitworth on 2 February 1946. Production had encompassed two Mk I prototypes, 3,425 Mk Is, 301 Mk lIs, 3,039 Mk Ills, 180 Mk VIIs and 430 Mk Xs, a total of 7,377 aircraft. These were built by Avro (3,673), Armstrong Whitworth (1,329), Austin Motors (330), Metropolitan Vickers (1,080), Vickers Armstrong (535) and Victory Aircraft (430). Some conversions between different mark numbers took place.

Statistics show that at least 59 Bomber Command squadrons operated Lancasters, which flew more than 156,000 sorties and dropped, in addition to 608,612 tons (618380 tonnes) of high explosive bombs, more than 51 million incendiaries. As the war in Europe was drawing to its close, plans were being made to modify Lancasters for operation in the Far East as part of Bomber Command's contribution to 'Tiger Force', but Japan surrendered before this could take place. A number of Lancasters were used to bring home prisoners of war from Europe, and various aircraft were modified for test flying in the UK and other European countries. Some were supplied to the French navy and others were converted for temporary use as civil transports, with faired in nose and tail areas, under the name Lancastrian. The Avro York transport used Lancaster wings and engines, plus a central fin in addition to the twin endplate fins.

A few Lancasters still survive, notably one airworthy example with the RAF Battle of Britain Memorial Flight and another used by the Canadian Warplane Heritage Museum in Canada.

Dam Busting Raids

Ruhr industry was dependent on hydroelectric power and water, supplied by several huge dams. The destruction of the largest of these would have a devastating effect on German armaments output. But no ordinary bomb was capable of the task. In the Weybridge offices of Vickers, a quiet genius called Barnes Wallis applied himself to the problem.

The solution he came up with was a large mine, which had to be placed with absolute precision against the inner face of the dams by flying at exactly 220 mph (354 km/h) and 60 ft (18 m), releasing the weapon to an accuracy of less than one fifth of a second. A special squadron was trained specifically for the task. To lead it, Wing Commander Guy Gibson was chosen, and his aircrews were hand-picked from the best that Bomber Command could offer. They were predominantly British, but included 26 Canadians, 12 Australians, two New Zealanders and a single American. It is less widely known that the ground crews and support tradesmen were also hand-picked. Thus was the birth of No. 617 Squadron at Scampton in March 1943.

The mine, codenamed Upkeep, was a large cylindrical weapon weighing 9,250 lbs (4200 kg), over two-thirds of which was high explosive. Aircraft were taken from squadrons in No.5 Group. The bomb bay doors were removed and special brackets fitted, together with an electric motor to get Upkeep rotating at 500 revolutions per minute before release. The bomb bay was faired to front and rear of the mine in order to reduce drag and the mid-upper turret was removed. Transformed in this manner, the Mk Is became Type 464 Provisioning Lancasters.

Other changes were made as they were found necessary. The entire raid was to be flown at low level, so bomb aimers assisted navigation using a specially prepared roller map. The nose turret had to be manned continually, which gave a role to the otherwise redundant mid-upper gunner, and stirrups were fitted to prevent him treading on the bomb aimer's head in moments of excitement.

Achieving the exact height over water at night proved difficult, but was solved by fitting Aldis lamps in the nose camera port and behind the bomb bay, angled so that the two spots of light touched at exactly 60 ft (18 m) and offset to starboard where they were easily seen by the navigator, who monitored height on the attack run.

Due to the low altitude required for the operation, standard bombsights could not be used. A simple device called the Dann sight was created in order to give the proper distance to target. It was made up from a plywood triangle, an eyepiece and a couple of nails or wooden dowels. The distance between two specific points on the dam was known, so the Dann sight was set up in such a fashion that when the nails or dowels lined up with these points, the correct distance was achieved for bomb release. Close control of the operation was vital, and for this Gibson had all Lancasters fitted with fighter-type VHF radios. This was the first use of the 'Master Bomber' technique, later to become standard throughout Bomber Command.

The Mohne Dam was known to be well defended, so it was assumed that the other targets were as well. Anticipating that the Lancasters would probably have to fight their way into and out of the target area, each gun was given three thousand rounds of tracer ammunition giving a total of 157 seconds firing time. By using all tracer ammunition it was hoped the Germans would over estimate the actual weight of fire and thus force them to keep their heads down.

Operation Chastise

The attack on the dams was set for the night of 16/17 May, when good weather was forecast the moon was full, and the water level behind the dams was at its highest. Nineteen Lancasters took off in three waves. The first wave consisted of nine aircraft in three Vics of three, led by Gibson. Its primary targets were the Mohne and Eder Dams. The second wave, of five Lancasters flying individually, took a more northerly route. Their target was the Sorpe Dam, of different construction to the first two and needing a different mode of attack, albeit with the same weapon. The third and final wave of five aircraft also flew individually. Taking off two hours after the others, it was a reserve to be used against the main targets if needed, otherwise to attack secondary dams in the area.

Opposition to the passage of the first wave was moderate, but Bill Astell's Lancaster fell to light flak. The remainder arrived over the Mohne Dam on time. Gibson later wrote, 'In that light it looked squat and heavy and unconquerable; it looked grey and solid in the moonlight, as though it were part of the countryside itself and just as immovable. A structure like a battleship was showering out flak all along its length'.

After circling to make an assessment of the situation, Gibson began his attack run, curving in down-moon, past the hills and low over the water. He had his spotlights on for height and the light flak saw him coming and opened up with everything they had. Bomb Aimer Spam Spafford released the mine and they swept low over the dam. From the air it looked like a perfect drop, but in fact the mine had fallen short.

Next came Hopgood, whose aircraft caught fire and crashed, while his mine bounced clear. Gibson then ordered Australian Mick Martin to attack. Martin's Lancaster was hit, and its mine was released off course to detonate harmlessly. Dinghy Young made a perfect run and deposited his Upkeep right against the dam wall. Even as Malt by made his run, the parapet crumbled and the dam burst. His mine added to the breach made by Young.

Eder Dam

Martin and Maltby headed for home, while Gibson and Young led the three remaining armed Lancasters to the Eder Dam. Australian David Shannon made three attempts without being able to line up correctly. Henry Maudslay then tried twice, with no luck. On Shannon's fourth attempt his mine exploded against the dam, causing a small breach. Maudslay tried once more, but his mine hit the parapet with him just above it. It was assumed that he and his crew died in the explosion, but badly damaged, he had limped some 130 miles (210 km) towards home before falling to flak.

Only one armed Lancaster remained, and on the second attempt its pilot, Les Knight, made a perfect run. His mine punched a hole clean through the giant dam wall. The fIrst aircraft to be lost during Operation Chastise was that of Eyers. Les Munro's Lancaster was damaged by flak had to abandon the mission, while Geoff Rice, flying as low as possible, hit the sea and lost his mine. He also was forced to return. Barlow, an Australian, was claimed by flak just inside the German border, and of the ill-fated second wave, only the American, Joe McCarthy,survived. After making nine runs against the Sorpe he dropped his mine on the tenth, but without any visible results.

The final wave fared only slightly better. Burpee, a young Canadian from Gibson's previous squadron, went down over Holland, while Ottley lasted only a little longer. Both fell to light flak. Of the other three, Anderson was the least lucky. Last off, the fates conspired to force him to abandon the mission without attacking.

Brown attacked the Sorpe after several attempts, like McCarthy with no visible result, while Townsend, on course for the Mohne Dam, was diverted to the Ennerpe Dam instead. After several brushes with flak, he emerged into an area made unrecognisable by floods from the already breached Mohne and Eder. Finally Townsend arrived at what appeared to be the Ennerpe and dropped his mine, but post-war evidence seems to indicate that he attacked the Bever Dam 5 miles (8 km) away.

The entire German air defence system was by now alert to the events. Apart from Maudslay, the only other loss was Dinghy Young. Hit by flak as he re-crossed the coast, be went down into the sea. Others, including McCarthy, Brown and Townsend, had eventful return flights, but recovered safely to Scampton.

Success had been expensive. Eight Lancasters failed to return home; of the 56 men on board, only three survived. Guy Gibson was awarded the Victoria Cross, Britain's highest decoration, and 33 other awards were made to participants in the raid. The Dams Raid has long passed into legend. No.617 Squadron had established itself as an elite unit.

A new role was sought for No. 617 Squadron. The modified Lancasters were replaced by standard Mk Ills, and the crews started intensive high and low level training. Wing Commander Guy Gibson was replaced by Squadron Leader George Holden. On 30 August 1943, the squadron was ordered to Coningsby for low-level attacks.

Dortmund-Ems

The next target was the well defended Dortmund-Ems canal, a strategic artery in the German transport system. No. 617 squadron was to try, using the new 12,000 lbs (5440 kg) high-capacity bomb. Low cloud in the target area caused the first attempt to be recalled, minus Maltby, who went into the sea after hitting someone's slipstream at low level. The next night they tried again. It was a disaster. Heavy mist in the target area foiled all attempts to bomb accurately, while the defences claimed five Lancasters, among them those of Holden and Les Knight. The squadron rapidly gained the reputation of being a suicide outfit. Six aircraft, with six more from No.619 Squadron, went out again the next night to attack the Antheor Viaduct in southern France at low level. This was another failure and the squadron was withdrawn from operations while changes took place.

One was the introduction of the Stabilizing Automatic Bomb Sight (SABS), introduced by Arthur 'Talking Bomb' Richardson, whom we last saw over Gdynia with Guy Gibson. No. 617 Squadron was now to become a medium and high-level 'sniper' squadron. The other was the arrival of Wing Commander Leonard Cheshire to command the unit on 11 November.

Cheshire was introspective and unconventional, and arguably the most inspirational bomber leader of the war. Always leading from the front, he was described by David Shannon as a pied piper; people followed him gladly. He set out to make the squadron live, breathe and eat bombing accuracy.

Several missions followed against pin point targets, but they were not a great success. Oboe marking was too inaccurate against small targets. Cheshire and Martin worked out between them that only low- level marking in a dive would be good enough, and on 3/4 January 1944, they tried it against a flying bomb site at Freval. By the illumination of flares, they marked from 400 ft (120 m), and 12,000 lbs (5440 kg) bombs from the remainder of the formation as they obliterated the target.

A more exacting test came on 8/9 February, by which time No.617 has moved to Woodhall Spa. The aero engine works at Limoges were almost totally destroyed, while damage to French houses close by was minimal. Other raids followed with equal success, the only failure during this time being another attempt against the Antheor Viaduct.

To mark heavily defended targets, smaller and faster aircraft were needed. The obvious choice was the De Havilland Mosquito, which Cheshire duly acquired, bringing the low-level marking career of the Lancaster to an end. At the same time, No. 617 became pathfinders and Main Force leaders to No.5 Group.

D-Day Deception

The first of these was Operation Taxable, a deception ploy that was designed to make the Germans think that a vast invasion fleet was moving towards Cap d' Antifer, some 20 miles (30km) north of Le Havre. This was done by 16 Lancasters, flying precise speeds and courses, dropping Window at five-second intervals. Packed with Window bundles, they maintained the deception for some eight hours until dawn broke to reveal only an empty sea to the expectant Germans.

The second was the introduction of the Tallboy, a new 12,000 lbs (5440 kg) bomb with exceptionally good ballistic qualities and penetrative power. Like Upkeep, Tallboy was the idea of Dr Barnes Wallis, and only the SABS equipped Dam Busters could bomb accurately enough to make the best use of this new and devastating weapon.

One of the few south-to-north rail routes still open in France at this time passed through a tunnel near Saumur, on the Loire. Shortly after midnight on 8/9 June the squadron arrived, and Cheshire placed two red spot fires in the mouth of the tunnel. Nineteen Tallboy armed Lancasters moved in, plus another six with conventional loads. The result was a series of enormous craters that tore the line to pieces. One Tallboy had impacted the hillside and bored its way down to explode inside the tunnel almost 60 ft (18 m) below, completely blocking it.

More precision raids followed such as the raids on the concrete E-boat pens at La-Harve and V-weapon sites scattered around Pas-de-Calais and elsewhere. In July, command of the squadron passed from Wing Commander Leonard Cheshire to Wing Commander Willie Tait DSO DFC.

The Tirpitz

The German battleship Tirpitz lying in Alten Fjord in Norway, tied down British naval units which would have been better deployed elsewhere. Even from the most northerly of British airfields Alten Fjord was outside Lancaster range. A deal was struck with the Russians, who made Yagodnik, near Arkhangelsk, available as a refuelling stop. For this and subsequent anti- Tirpitz opera- tions, No.617 was joined by No.9 Squadron, which, although fitted with the Mk XIV vector bombsight, was also something of an elite outfit. Of the 36 Lancasters detailed, 24 carried Tallboys; the others were loaded with 12 Johnny Walker Diving Mines each, an original but ineffective weapon.

The raid nearly ended in disaster when bad weather over Russia forced many Lancasters to land where they could. Six were abandoned in the marshes. On 15 September the attack was finally mounted, and the German early warning system proved equal to the task and a smokescreen quickly obscured the battleship. A single Tallboy hit was scored, but Tirpitz was still afloat. The Kriegsmarine moved her south to Tromso Fjord for use as a floating German gun battery; she would never sail again, but this was not known either.

Calculations showed that fitting internal fuel tanks in the fuselage of the Lancasters would allow Tirpitz to be attacked from Lossiemouth. On 20 October, 40 aircraft of Nos. 617 and 9 Squadrons set out on the long haul to Tromso. A combination of poor weather and enemy fighters made this attack a failure, and few crews even so much as saw the battleship.

Specifications (Avro 683 Lancaster B.Mk I & III)

Type: Seven or Eight Seat Heavy Bomber

Accommodation/Crew: A crew of seven consisting of the Pilot, Flight Engineer, Observer/Nose Gunner/Bomb-aimer, Navigator, Radio/Wireless Operator, Mid-Upper Gunner, and Tail Gunner. The Bomb-aimer was in the nose position below the front turret. Above and behind and to the port is the Pilot's position in a raised canopy with good all-round vision and armour plating on the back of the seat and armour protection behind his head. Inside the canopy immediately aft of the pilot's seat is the Fighting Controller's position and is provided with special bullet-proof glass. Slightly aft of this position is the Navigator's position, with table, chart stowage and astral done in the roof. At the rear end of the navigator's table and just forward of the front spar is the Radio Operator's station. Within the centre-section is a restroom with a bed. Aft of the rear spar is the mid-upper and mid-lower turrets, together with various equipment stowage for flares, emergency rations, etc. A dinghy is carried in the centre-section trailing-edge portion of the wing and is automatically deployed and inflated upon impact with water. It can also be operated by hand. In the extreme tail is the rear turret. A walkway is provided along the entire length of the fuselage and the main entrance door is situated on the starboard side just forward of the tailplane.

Design: Chief Designer Roy Chadwick and Managing Director Roy Dobson of A. V. Roe Aircraft Company Limited based on the Avro 679 Manchester design

Manufacturer: Alexander V. Roe (Avro) Aircraft Company Limited based in Greengate, Middleton (Chadderton), Manchester with another production facility located at Yeadon. Prior to 1938, the main plant was located in Newton Heath, but in the spring of 1939 the company moved its main office to the new, much larger facility in Greengate. In order to further expand production capability, Metropolitan Vickers Limited of Trafford Park (Manchester), Armstrong Whitworth Limited of Baginton and Bitteswell (Coventry), Austin Motors of Longbridge (Birmingham), Vickers Armstrong of Chester and Castle Bromwich and Victory Aircraft of Canada (Malton, Ontario) also built the aircraft. A large number of sub-contractors were also involved in component manufacture.

Powerplant: (B.Mk I) Initially four Rolls-Royce Merlin XX or 22 Vee 12-cylinder liquid-cooled inline engines each rated at 1,280 hp (955 kW) for take-off and 1,240 hp (925 kW) at 2,850 rpm at 10,000 ft (3050 m) with a maximum power rating of 1,480 hp (1104 kW) at 3,000 rpm at 6,000 ft (1830 m). Late production B.Mk I aircraft being equipped with four Rolls-Royce Merlin 24 Vee 12-cylinder liquid-cooled inline engines rated at 1,620 hp (1209 kW) for take-off and 1,240 hp (925 kW) at 2,850 rpm at 10,000 ft (3050 m) with a maximum power rating of 1,640 hp (1223 kW) at 3,000 rpm at 2,000 ft (610 m). (B.Mk II) Four Bristol Hercules VI 14-cylinder two-row air-cooled radial engines rated at 1,615 hp (1205 kW) for take-off and 1,675 hp (1250 kW) at 2,900 rpm at 4,500 ft (1370 m) with a maximum power rating of 1,675 hp (1250 kW) at 2,900 rpm at 4,500 ft (1450 m). The radial engined Lancasters had a higher top speed but also had a higher fuel consumption. (B.Mk III) Four American-built Packard Merlin 28 Vee 12-cylinder liquid-cooled inline engines each rated at 1,300 hp (970 kW) for take-off, or four American-built Packard Merlin 38 (Merlin 22) Vee 12-cylinder liquid-cooled inline engines each rated at 1,390 hp (1037 kW) for take-off. Some later B.Mk III aircraft had the American-built Packard Merlin 224 (Merlin 24) Vee 12-cylinder liquid-cooled inline engines each rated at 1,620 hp (1209 kW) for take-off. All Merlin engines used a mechanically driven, two-speed, single stage, centrifugal supercharger. Note: Rolls-Royce engine marks up to XX (twenty) are distinguished by Roman numbers, while marks above that were distinguished by Arabic numericals.

Propellers: Hamilton-Standard or Rotol propellers. In later aircraft paddle-bladed Nash-Kelvinator propellers were used increasing the cruising speed by 8 mph (12.9 km/h) and the service ceiling by 1,500 ft (457 m). The airscrew shaft was a SBAC No. 5 type with a reduction gear ratio of 0.42:1.

Performance: (Early B.Mk I) Maximum speed 275 mph (443 km/h) at 15,000 ft (4572 m). (Late B.Mk I) Maximum speed 287 mph (462 km/h) at 11,500 ft (3505 m), 275 mph (443 km/h) at 15,000 ft (4572 m), 260 mph (419 km/h) at 19,400 ft (5913 m); cruising speed 234 mph (377 km/h) at 21,000 ft (6401 m), 200 mph (322 km/h) at 15,000 ft (4572 m); stalling speed (clean) 95 mph (153 km/h) at 60,000 lbs (27211 kg); normal service ceiling 23,000 ft (7010 m), nominal service ceiling 24,500 ft (7468 m); absolute service ceiling 24,671 ft (7500 m); climb to 20,000 ft (6096 m) in 41 minutes and 40 seconds; initial rate of climb 250 ft (76 m) per minute with full bombload. In a hard dive the prototype aircraft achieved speeds reaching almost 400 mph (644 km/h) with production aircraft (operational loadout) being limited to 360 mph (578 km/h).

Carburetion (Merlin): SU float carburettor, type AVT 40 / 241 / 216 / 224 / 227. American built Packard Merlins had the Bendix Stromberg pressure-injected type.

Ignition (Merlin): Two BTH C.5 SE12-S or Rotax NSE12-4 magnetos.

Fuel Capacity / Specification: A total of six fuel tanks consisting of two 580 Imperial gallon (703 US gallon or 2637 litre) inboard tanks, two 383 Imperial gallon (464 US gallon or 1740 litre) intermediate tanks and two 114 Imperial gallon (138 US gallon or 518 litre) outboard tanks giving the aircraft a total fuel capacity of 2,154 Imperial gallons (2,610.6 US gallons or 9790 litres). Provisions for one or two overload fuel tanks of 400 Imperial gallons (485 US gallons or 1818 litres) each could be carried in the bomb bay. Fuel specification 100 / 130 Grade DED 2475 (AN-F-28).

Coolant Capacity / Specification: 5 Imperial gallons (6 US gallons or 22.7 litres) per engine made up of 70 percent water + 30 percent ethylene glycol to specification DTD 344 A.

Oil Capacity / Specification: Each engine had its own oil tank in the nacelle with a capacity of 37.5 Imperial gallons (45.4 US gallons or 170.25 litres) for a total of 150 Imperial gallons (181.6 US gallons or 681 litres). Oil specification DED 2472 / B / O.

Range (typical): 2,530 miles (4072 km) with a bombload of 7,000 lbs (1795 kg); 1,730 miles (2786 km) with a bombload of 12,000 lbs (5442 km); 1,550 miles with a bombload of 22,000 lbs (9977 kg).

Weights & Loadings: Empty (clean) 39,600 lbs (16740 kg), empty (equipped) 53,300 lbs (24040 kg) with a maximum take-off weight of 65,000 lbs (29480 kg). The B.Mk I Special had a maximum take-off weight of 70,000 lbs (31751 kg) while carrying a 22,000 lbs (9980 kg) Grand Slam bomb. Wing loading 52.7 lbs/sq ft (258 kg/sq m); power loading 13.3 lbs/hp (6.35 kg/hp).

Dimensions: Span 102 ft 0 in (31.09 m); length 69 ft 6 in (21.18 m); height 20 ft 6 in (6.25 m); wing area 1,297.0 sq ft (120.49 sq m); tailplane area: 237.0 sq.ft (22.0 sq m); tail fin and rudder area: 111.40 sq ft (10.35 sq m); aileron span 17 ft 3 in (5.3 m).

Gunsights: The main gunsight used in Lancaster turrets was the Barr & Stroud G Mk Ill reflector sight. In use the screen was mounted at a 45 degree angle showed an illuminated orange circle with a central dot, both focused at infinity. A brightness control adjusted it according to conditions; bright in sunlight, dim at night. The radius of the circle was approximately equal to the wingspan of a single-engined fighter at a range of 1,200 ft (365 m), while the radius of the circle gave the deflection (the amount of aiming ahead) needed to hit a target with a relative crossing speed of 50 mph (80 km/h). In 1944, the Mk llc gyroscopic sight entered service as a turret sight. This could actually predict the point of aim, if the approaching fighter could be tracked for a short while, and its wingspan set on a dial.

Defensive Armament: A total of ten 7.7 mm (0.303 in) Browning machine-guns in a nose, mid-upper, tail and ventral position. The ventral position was soon deleted on most RAF Lancasters as it was thought unnecessary and took the same position as the H2S radome. Where possible, and unofficially, many crews installed a single 7.7 mm (0.303 in) or 12.7 mm (0.50 in) Browning machine-gun on aircraft lacking the ventral turret in order to deal with the ever increasing 'behind and below' attacks of German night fighters using Schräge Musik, which interesting, did not use tracer ammunition. These were hastily installed configurations usually consisting of the gunner sitting on a bicycle type seat with the ammunition box being bolted to the floor and the gun mounted in a hole cut into the floor. The British would eventually re-introduce the F.N.64 turret on aircraft equipped with G-H radar (an improved version of Gee) since that type of radar did not have the large radome as the H2S required. During 1943/1944 when the use of Schräge Musik on german Nachtjagd (night fighters) became widespread, the new twin-gun F.N.64 power-operated turrets became the most important gun position on the bomber. On aircraft that were modified to carry the "Tall Boy" or "Grand Slam" bombs, most had the nose and mid-upper turrets were removed and the tail turret reduced to a single pair of 7.7 mm (0.303 in) Browning machine-guns in order to reduce weight. The 7.7 mm (0.303 in) ammo consisted of Ball, Tracer, Armour Piercing and Incendiary.

• 2 × 7.7 mm (0.303 in) Browning Mk II trainable forward-firing machine-guns in the power-operated Frazer-Nash F.N.5A nose turret with 1,000 rounds per gun using a Barr & Stroud G Mk III reflector sight.
   

• 2 × 7.7 mm (0.303 in) Browning Mk II trainable machine-guns in the power-operated Frazer-Nash F.N.50 (Boulton-Paul) dorsal turret with 1,000 rounds per gun using a Barr & Stroud G Mk IIIA reflector sight.
   

• 4 × 7.7 mm (0.303 in) Browning Mk II trainable rearward-firing machine-guns in the power-operated Frazer-Nash F.N.20A tail turret with 2,500 rounds per gun using a Barr & Stroud G Mk III reflector or Gyro Mk IIc sight.
   

• 2 x 7.7 mm (0.303 in) Browning Mk II trainable rearward firing machine-guns in a power-operated Frazer-Nash F.N.64 ventral turret with 500 rounds per gun using a periscopic sight. (This position did not have a dedicated gunner).

Offensive Ordnance: Up to 8,000 lbs (3629 kg) of bombs carried in a 33 ft (10.0 m) long under fuselage internal bomb bay. While capable of carrying much more weight, early aircraft were limited to 8 x 1,000 lbs (454 kg) GP/MC (General Purpose Medium Capacity) bombs due to the physical restrictions of the bomb bay, but continued improvements enabled later production aircraft to carry up to 14,000 lbs (6350 kg) of bombs normally, including 2,000 lbs (907 kg) AP (Armour Piercing) or HE/SAP (High Explosive Semi-Armour Piercing) bombs, 4,000 lbs (1814 kg) HE/HC (High Explosive High Capacity) 'Block Buster' (also called a "Cookie") and a single 8,000 lbs (3628 kg) HE/HC (High Explosive High Capacity) bomb. Some aircraft underwent special modifications to allow them to carry the 12,000 lbs (5443 kg) HE/DP (High Explosive Deep Penetration) 'Tall Boy', the 12,000 lbs (5443 kg) HE/HC (High Explosive High Capacity) 'Factory Buster' and the 22,000 lbs (9979 kg) HE/DP (High Explosive Deep Penetration) 'Grand Slam' bombs. The 12,000 lbs (5443 kg) HE/HC 'Factory Buster' was actually three 4,000 lbs (1800 kg) HC High Explosive "Cookies" bolted together given the bomb a total of 5,200 lbs (2358.7 kg) of Torpex 'cemented' within a 1 inch (25.4 mm) jacket of TNT. Aircraft capable of carrying the larger 4,000 lbs (1800 kg) and 8,000 lbs (3629 kg) bombs can easily be identified by the use of a bulged bomb bay door. Standard loadouts were as follows:

• Blast & Demolition - 1 x 8,000 lbs (3628 kg) HE plus up to 6 x 500 lbs (227 kg) HE bombs.
   

• Blast & Demolition - 14 x 1,000 lbs (454 kg) bombs.
   

• Blast, Demolition & Fire - 1 x 4,000 lbs (1814 kg) HE 'Cookie' plus 3 x 1,000 lbs (454 kg) HE bombs plus up to 6 SBC (Small Bomb Cannisters) each holding either 236 x 4 lbs (1.8 kg) or 24 x 30 lbs (13.6 kg) incendiaries.
   

• Blast, Demolition & Fire - 1 x 4,000 lbs (1814 kg) HE 'Cookie' plus up to 12 SBC (Small Bomb Cannisters) each holding either 236 x 4 lbs (1.8 kg) or 24 x 30 lbs (13.6 kg) incendiaries.
   

• Maximum incendiary - 14 SBC (Small Bomb Cannisters) each holding either 236 x 4 lbs (1.8 kg) or 24 x 30 lbs (13.6 kg) incendiaries.
   

• Deployed Tactical Target - 1 x 4,000 lbs (1814 kg) HE 'Cookie' plus up to 18 x 500 lbs (227 kg) HE bombs.
   

• Low Level Attack - 6 x 1,000 lbs (454 kg) HE bombs with delayed action fuses.
   

• Hardened Targets & Ships - 6 x 2,000 lbs (907 kg) AP bombs with very short fuses.
   

• Mine Laying - Up to 6 x 1,500 lbs (680 kg) or 1,850 lbs (839 kg) parachute sea mines which could be either acoustic or magnetic. First used on the night of 3/4 March 1942.

Variants: BT308 (first prototype), DG595 (second prototype), B.Mk I, B.Mk I Special (Grand Slam), B.Mk I FE (Far East), B.Mk II (Hercules engines), B.Mk III, B.Mk III Type 464 Special (Dambuster), B.Mk IV (renamed Lincoln Mk I), B.Mk V (renamed Lincoln Mk II), B.Mk VI, B.Mk VII, B.Mk VIII FE (Far East), B.Mk X (Canadian Built).

Equipment/Avionics: The Mark IXA Course-Setting Bomb Sight (CSBS) and the Mark XIV Computing Bomb Sight (CBS) were standard. The Radio section is complete with a Marconi Transmitter T.1154 and Receiver R.1155 with a Morse key on the right of the wireless operators table. The operator was also provided with a switching gear to connect crew positions to the receiver or transmitter if required. H2S "Fishpond" Indicator 182 aircraft detection display plus all the auxiliary equipment. The Navigators section contains the Gee & Oboe radio guidance navigation equipment, H2S main blind bombing/mapping radar with the PPI (Plan Position Indicator) plus all the navigation aids used prior to the introduction of the Gee, Oboe & H2S radars. An improved H2X radar would replace the older H2S radar after German FuG 350 Naxos Z radar equipped night fighters could home in on the H2S radar transmissions. Some aircraft used the "Monica" tail mounted early warning radar which was effective to a range of about 1,000 yards, but had no IFF (Identification Friend or Foe) capability. Monica was discontinued in use when it was discovered that German FuG 227 Flensburg radar equipped night fighters could actually home in on the transmission signal given out by the Monica radar. Rebecca navigation radar was also used on small numbers of aircraft. Boozer early warning radar (ground and air) was also used and considered better than Monica. Tinsel was an electronic warfare jamming device which in its early use was successful, but German response to the device limited later effectiveness. An automatic gun-laying apparatus (A.G.L.T) code-named 'Village Inn' was fitted to the F.N.121 tail turret to allow radar guided beyond visual range firing. The device although potentially devastating, it originally lacked the ability to distinguish between Friend or Foe. The aircraft is also fully equipped for night flying. An F.24 camera was standard equipment for vertical photography to confirm bombing accuracy.

A Frazer-Nash FN.5 nose turret with two 7.7 mm (0.303 in) Browning Mk II machine-guns

Wings/Fuselage/Tail Unit: The wings are of a mid-wing cantilever monoplane type. The wing is made up of five main sections, comprising a centre-section of parallel chord and thickness which is integral with the fuselage centre-section, two tapering outer sections and two semi-circular wing-tips. Subsidiary wing units consist of detachable leading and trailing-edge sections of outer wings and centre-section, flaps and ailerons. All units are built up individually with all fittings and equipment before assembly. Two-spar wing structure, each spar consisting of a top and bottom extruded boom bolted on to a single thick gauge webplate. Ribs are aluminium-alloy pressings suitably flanged and swaged for stiffness. The entire wing is covered with a smooth aluminium-alloy skin. Ailerons on outer wing sections have metal noses and are fabric covered aft of the hinges. Trimming tabs in ailerons. Split trailing-edge flaps between ailerons and fuselage. The fuselage in an oval all-metal structure in five separately assembled main sections. The fuselage backbone is formed by pairs of extruded longerons located halfway down the cross-section of the three middle sections. Cross beams between these longerons support the floor and form the roof of the bomb compartment. "U"-frames and formers bolted to the longerons carry the smooth skin plating. The remaining sections are built up of oval frames and formers and longitudinal stringers, covered with flush riveted metal skin. All equipment and fittings are installed before final assembly of the separate units. The tail unit is a cantilever monoplane type with twin oval fins and rudders. Tailplane in two sections built up in similar manner to the wings, the tailplane spars being joined together within the fuselage on the centreline. Tailplane, fins and rudders are metal covered with the elevators covered in fabric. Trimming tabs in elevators and rudders.

Landing Gear: The main landing gear was retractable with a fixed tailwheel. Main wheels are hydraulically retracted into the inboard engine nacelles and hinged doors connected to the retracting gear close the apertures when the wheels are raised. The main landing wheels have a track of 23 ft 9 in (7.24 m).

History: First flight (prototype BT308) 9 January 1941; first flight (prototype DG595) 13 May 1941; first flight (Mk II prototype BT310) 26 November 1941; first flight (Canadian B.Mk X) 6 August 1943; last new delivery (Mk I (FE) serial TW910) 2 February 1946; last aircraft retired from RAF service (MR.Mk III) February 1954.

Operators: United Kingdom (RAF & BOAC), Canada (RCAF), Australia (RAAF), New Zealand (RNZAF), Poland (Free Polish Squadron serving with the RAF). Post-war operators included Argentina, France (Aéronavale), Egypt and Sweden.

Units: The Lancaster equipped Nos. 7, 9, 12, 15, 35 (Madras Presidency), 44 (Rhodesia), 49, 50, 57, 61, 83, 90, 97 (Straits Settlements), 100, 101, 103, 106, 109, 115, 138, 149 (East India), 150, 153, 156, 166, 170, 186, 189, 195, 207, 218 (Gold Coast), 227, 514, 550, 576, 582, 617 (Dambuster), 619, 622, 625, 626, 630 & 635 RAF Bomber Command Squadrons. The Lancaster initally entered service with No. 44 (Rhodesia) Squadron based at Waddington followed by No. 97 Squadron and then No. 207 Squadron. No. 300 (Masovian) was an all Polish Squadron serving with the RAF. Squadron No. 101 was a special unit whose aircraft could be distinguished externally by three large aerials on top of the fuselage. They carried the top secret ABC (Air-Borne Cigar) from October 1943 onwards. ABC was a jammer working on the German night fighter frequency, and required an additional member of the crew to operate it. Lancasters of No. 101 Squadron carried a full load of bombs and scattered throughout the bomber streams, accompanied the Main Force on nearly every raid. In the later stage of the war, with multi-pronged raids becoming the norm, 101 Squadron would become the largest Lancaster squadron of all, with a final complement of 42 aircraft.

Royal Canadian Air Force Squadrons No. 405 (Vancouver), 408 (Goose), 419 (Moose), 424 (Tiger), 426 (Thunderbird), 427 (Lion), 428 (Ghost), 429 (Bison), 431 (Iroquois), 432 (Leaside), 433 (Porcupine), 434 (Bluenose) Squadrons all equipped the Lancaster. The Royal Australian Air Force equipped three squadrons Nos. 460, 463 & 467 and the Royal New Zealand Air Force equipped No. 75 Squadron with Lancasters.

Number Built: 7,366

Number Still Airworthy:  Two