The Avro Lancaster went on to become the most important British heavy bomber or World War 2. Interestingly, its success was born from the failure of the Avro Manchester bomber - a twin-engined heavy bomber first flown in July of 1939 and adopted in November of 1940. The type was hampered by unreliable engines that led to only 202 examples being produced in all. The Lancaster was born from this failed design to include different engines set along a revised wing. The prototype version was nothing more than a revised Manchester complete with its triple vertical finned tail unit - the key difference lay in the selection of the Rolls-Royce Merlin X series inline piston engines of 1,145 horsepower each. Within time, the triple-finned tail unit was given up in favor of the standard twin rudder arrangement common to the Lancaster history.
In its prototype form, the Lancaster went airborne for the first time on January 9th, 1941. With World War 2 in full swing and the British commitment extensive, the prototype was quickly handed to Boscombe Down for formal evaluations. Development was so speedy that a production-quality form was airborne as early as October 1941 and the series, upon passing its requisite trials, was adopted for operational service in February of 1942, quantitative orders forthcoming. Early production versions were born for Manchester airframes still on Avro lines and inducted into RAF service as the Lancaster B.Mk I.
With production in full swing, the Lancaster was immediately placed into frontline action. Each aircraft required a standard operating crew of seven to include the pilot, bombardier, navigator, flight engineer, radio operator, dorsal gunner and rear gunner. Each man was specifically trained for their respective positions about the craft that ranged from the nose to the tail. The bomb bay was given much of the central internal volume. The flight deck consisted of a heavily glazed canopy with conventional seating and controls. The nose was equally glazed over to provide the bombardier and his equipment unfettered views of the action ahead and below. The undercarriage incorporated two main landing gear legs (single wheeled) with a tail wheel at rear. Outwardly, the Lancaster followed the same design style of other British bomber aircraft of the war, nothing beautiful but full of business. Original Lancasters showcased a bomb bay initially intended to carry up to 4,000lbs of ordnance. During the height of the war, a typical Lancaster set off with approximately 14,000lbs of conventional drop bombs and eventually even fielded the massive 22,000lb "Grand Slam" bombs (their size forced the bomb bay doors to be removed altogether).
Beyond its bomb load out for its offensive armament, the Lancaster was outfitted with no fewer than 8 x 7.7mm Browning machine guns for self-defense across three Frazer-Nash hydraulically-powered turrets at the nose, dorsal spine and tail. Two were installed in a nose/chin turret and operated by the bombardier. Two were fitted to the dorsal turret at amidships along the fuselage spine. Four were installed in a powered tail turret at the extreme aft of the aircraft. Unlike its American brethren, the Lancaster series (on the whole) lacked a belly turret and beam waist gunners for additional defense and utilized a smaller-caliber (7.7mm/0.303) machine gun (as opposed to 0.50 caliber). At one point, the thought of adding a belly turret as standard was entertained but never followed-up. Only a small number of early-form Lancasters were outfitted with ventral turrets (these armed with 2 x 0.303 machine guns).
The need for capable Lancasters was such that its production was tied to other much-needed aircraft meaning that there proved a near-shortage of available Merlin engines threatening manufacture. To supplement stocks of Rolls-Royce Merlins, the American concern of Packard was brought into the fold to produce the same powerplant in the United States (under license). In extreme circumstances, the RAF took on Lancasters fitted with Bristol Hercules VI/XVI radial piston engines of 1,735 horsepower. As Melin engines themselves evolved so too did the various Lancasters coming off the assembly lines - new mounts included the Merlin XX, 22 and 24 series.
Lancasters began their operational careers under rather mixed results. Daylight raids without escort fighters in tow guaranteed ruin for bomber crews as enemy fighter patrols and interceptors coupled with ground-based FlaK fire could cut through Lancaster formations with relative impunity. On one early such raid, Lancasters managed to find their mark on German targets in Augsburg but lost seven of its twelve aircraft in the process. This forced Bomber Command to take the fight to the night skies to which Lancaster crews showcased their mettle. Daylight raids were now protected by escorting fighter groups which allowed for higher success rates in terms of returning crews.
Lancasters were credited with the sinking of the German KMS Tirpitz battleship when, on November 12th, 1944, two Lancaster groups engaged the vessel at Tromso Fjord in Norway with special 12,000lb "Tallboy" bombs designed specifically for armored targets. The battleship was appropriately sunk and a total loss for the shrinking German Navy. In similar-minded sorties, the "Grand Slam" mega-bomb came into play and targeted fortified underground positions, the 22,000lb creation sufficient in cutting through and disrupting the integrity of the concrete structures. The "Upkeep" series was a 9,250lb design intended for the destruction of dams.
Lancaster bombers formed some 59 Bomber Command squadrons and were credited with 156,000 bombing sorties in the whole course of the war, dropping some 681,600 tons (short) of ordnance.
The Lancaster served beyond the British and their RAF, seeing operational service (some during World War 2 and others in the post-war years) with Argentina, Australia, Canada, Egypt, France, Poland, the Soviet Union (via Lend-Lease) and Sweden. Production netted 7,377 units by February 2nd, 1946 when the last airframe was handed over to the RAF from Armstrong Whitworth. The final operational Lancaster was retired from Canadian service in 1963, some two decades since its introduction. Canada produced Lancasters under the B.Mk X (Lancaster B.Mk III) and B.Mk XV (Lincoln B.Mk I) designations.
The Lancaster series was produced in a few notable variants though the original Merlin XX-equipped B.Mk I models (later with Merlin 22 and 24 engines) survived through to the end of the war in 1945. The PR.Mk 1 was a photographic reconnaissance platform sans its guns and turrets and bomb-carrying capability. The B. Mk I (FE) was a tropicalized form intended for Far East actions against the Japanese. The B.Mk II incorporated the Bristol Hercules engines with 300 examples completed by Armstrong Whitworth. B.Mk III was used to signify B.MK I models completed with American Packard engines. The ASR.Mk III was a B.Mk III bomber model appropriately modified with lifeboat and detection antenna for the Air-Sea Rescue (ASR) role. The GR.Mk 3 was a maritime reconnaissance platform version of the B.Mk III series. The B.IV was given a lengthened fuselage with widened wings ad Boulton Paul powered turret with 2 x 12.7mm Browning heavy machine guns with power served through concurrent Merlin 85/68 engines. Such a difference was this mark that it became the Lincoln B.Mk I and this was followed by the B.Mk V becoming the Lincoln B.Mk II with widened wings and an even longer fuselage with Merlin 85 engines. Final production Lancasters became the B.Mk VII with revised armament.
Performance specifications for the definitive B.Mk I model included a top speed of 282 miles per hour, cruise speed of 200 miles per hour, range of 2,530 miles, service ceiling of 21,400 feet and a rate-of-climb nearing 720 feet per minute.