Roy Chadwick's four-engined heavy bomber provided Royal Air Force's Bomber Command with the aircraft it needed to wage its strategic bombing campaign. 'The Lanc', as it was also known, is perhaps best known for taking part in 'Operation Chastise', better known as the Dambusters raid, during the Second World War. It would spend fifteen years in RAF service fulfilling a number of different roles before its retirement.

With the twin-engined Avro Manchester in production, but yet to enter service, Avro met with the Air Ministry on the 20th February 1940 to discuss a four engined version of the Manchester. The Manchester at that time was powered by the Rolls-Royce Vulture, however the need for Rolls-Royce's Merlin engines during the Battle of Britain and reliability issues with the Vulture meant manufacturing of the engine would eventually be stopped after 538 had been produced. During September 1940 Avro got the green light from the Air Ministry on what was known at that time as the Manchester Mk III.

The prototype aircraft would be powered by four 1,145-hp Rolls-Royce Merlin X engines which lead to the increase of the wing span. Flying from RAF Ringway on the 9th January 1941, with the aircraft now known as the Lancaster, with H.A. 'Bill' Thorn at the controls the aircraft was a big improvement and on the 27th January it was sent to the Aircraft and Armament Experimental Establishment based at Boscombe Down, where it would undergo intensive trials. No. 44 Squadron at RAF Waddington would receive the prototype during September 1941 to undergo evaluation and for crew training. The second Lancaster prototype flew on the 13th May 1941 and was powered by Merlin XX engines and featured a twin-finned tail layout with the third central fin now removed and it was this prototype that production models would derive from. The second prototype was also sent to the A&AEE where during a dive the Lancaster reached 360 mph.

Proving an instant success, an initial contract for 1,070 Lancasters was placed with more orders following. Due to the increased speed of development, as a result of wartime urgency, the first production version flew on the 31st October 1941 and Avro Manchesters still in production were converted to Lancaster Mk Is although from 1942 they were re-designated Lancaster Mk B.I. However due to the influx of orders other companies took on production of the new aircraft to take the pressure of the company's Cheadderton and Yeadon factorys as they couldn't keep up with the demand for the Lancaster.

The production Lancaster Mk B.Is were fitted with 1,280-hp Merlin XX engines giving the aircraft a top speed of 287 mph, range of 2,530 miles with a service ceiling of 24,500 ft. The range and service ceiling were a vast improvement on the Manchester. Armament consisted of three Frazer-Nash turrets which totalled eight machine-guns, four in the tail turret and two each for the nose and dorsal turrets. Bomb load was 14,000lb. No. 44 Squadron was the first to be equipped with the new aircraft on the 24th December 1941. They also used the Avro Lancaster for its first operational mission when they laid mines in the Heligoland Bight on the 3rd March 1942.

It was not until five month later that the general public were informed of this new aircraft when on the 17th August twelve Lancasters from Nos. 44 and 97 Squadron attacked a u-boat diesel factory in Augsburg, Germany. The raid itself was to confirm that sending heavy bombers on unescorted daylight sorties was unfeasible as of the twelve Lancasters sent on the raid only five returned. During this raid Squadron Leaders John Nettleton and John Sherwood were both awarded the Victoria Cross. The following day saw Bomber Command's new Pathfinder force undertake its first operation when Flensburg, Germany was attacked and No. 83 Squadrons Lancaster B.Is would be involved in marking the target. The operation was a failure as winds took the bomber force off course and areas of Denmark were mistaken for Flensburg.

With the Avro Lancaster rolling of the production line in sufficient numbers they soon began to replace the Manchester, however as with a number of other aircraft the Lancaster relied on Merlin engines and as a result the Merlin engine was in danger of becoming in short supply. So to counteract this a Lancaster Mk B.II prototype was proposed and this used four 1,650-hp Bristol Hercules VI or XVI radial engines and flew for the first time on the 26th November 1941.

The Lancaster Mk B.II had a top speed of 270 mph, range of 2,250 miles, service ceiling of 18,500 ft and armament consisted of eight 0.303-in machine-guns and 14,000lb bombs. The first production example flew on the 2nd September 1942, that same month three Mk B.IIs from the first production batch were sent to the Aircraft and Armament Experimental Establishment and nine were sent to equip No. 61 Squadron based at RAF Syerston. This squadron was to perform service trials and had previous experience with the Lancaster after formally being a Lancaster Mk I squadron. Minor problems with the aircraft were experienced during the early part of its operational use. The Mk B.II made its operational debut on the 11th January 1943 when two took part in a raid on Essen, Germany and during its six months with No. 61 Squadron they did not lose any of the planes assigned to them.

One of the main drawbacks of the Bristol Hercules powered Mk B.II was its low service ceiling and it was the slowest of all the Lancaster variants and after 301 had been produced, production was ended. The Mk II flew its last mission on the 23rd September 1944 with No. 514 Squadron and although a few remained in service, even into the post-war era, they were mainly used as test-beds and the last Mk B.II was scrapped in 1950.

The next Lancaster Mk was the B.III powered by Packard built Merlin engines it also featured minor changes to the equipment and the bomb aimer's 'bubble' was enlarged and this would be produced alongside the Merlin engined Lancaster Mk B.I. The Mk B.III had a top speed of 287 mph, range of 2,530 miles and a service ceiling of 24,700 ft. Armament consisted of eight 0.303-in machine-guns and upto 22,000lb bombs. It was to be the Mk B.III, which was modified to carry the Barnes-Wallis designed 'Bouncing Bomb', which was used for the 'Dambusters' raid, officially known as 'Operation Chastise', when on the 16th/17th May 1943 Lancasters of No. 617 Squadron led by Wing Commander Guy Gibson, and having to drop their bombs from just 60ft, attacked the Mohne, Eder and Sorpe dams breaching the first two and causing minor damage to the third, this came at a heavy price as of the nineteen aircraft sent out eight failed to return with 3 aircrew taken prisoner and 53 killed.

The Mk B.VI was next, the two Lancaster Mk's before this the Mk B.IV and B.V had been redesigned so much they were renamed the Avro Lincoln B.1 and B.2 respectively, and it was suggested to use either of the Merlin 85 or 87 engines. As a result Rolls-Royce received nine airframes for comparative tests. Several of these airframes were used by No. 635 Squadron operationally as Pathfinders with a improved H2S radar bombing aid and early electronic countermeasures equipment and both nose and dorsal turrets removed. But despite showing much improved performance over early Lancasters none were produced and was removed from service in November 1944, with the aircraft used for a number of different tests and experiments.

The Canadian built Lancaster Mk B.X was next powered by Packard built Merlin engines it was similar to the Mk B.III with instrumentation and electronics which were Canadian and US built and the armament for this plane was fitted once the aircraft arrived in the UK and the 6th August 1943 saw the first example fly. The final production Avro Lancaster was the Mk B.VII which was powered by the 1,620-hp Rolls-Royce Merlin 24 which gave the aircraft a top speed of 275 mph, range of 2,350 miles and a service ceiling of 25,000 ft. Armament was changed with a American Marin dorsal turret with its two 0.50-in machine-guns replacing the Frazer-Nash turret which had two 0.303-in machine-guns. The Marin turret was also placed further forward compared to previous Mks with six 0.303-in machine-guns, two in the front and four in the rear complementing this.

The Lancaster's development progressed alongside the bombs available at the time. This can be seen in the development of the Lancaster's bomb-bay originally able to carry bombs of 4,000lb then 8,000lb and eventually the 12,000lb or 'Tallboy' bomb and finally the 22,000lb 'Grand Slam', the latter two bombs were also designed by Barnes Wallis.

As the Lancaster started to enter service in larger numbers it would become Bomber Command's main bomber and equipped at least 59 squadrons and alongside the Handley Page Halifax and Short Stirling would take part in Bomber Command's strategic bombing campaign against Germany during 1942 – 1945. This included a number of operations such as the Battle of the Rhur between the 5th March 1943 - 1st July 1943, which saw 18,506 sorties undertaken with the loss of around 5,000 aircrew, and the Battle of Berlin between the 19th November 1943 - 31st March 1944 which saw 2,690 aircrew lose their lives during 9,111 sorties.

The Lancaster also took part in 'Operation Crossbow', originally 'Operation Bodyline', which ran from the 17th August 1943, when Peenemunde, Germany was attacked and this raid was known as 'Operation Hydra', to the 2nd May 1945, targeting the German V-1 and V-2 programs. It would also play a part in attacking vital targets in France in the run up to D-Day

Another important task given to the Avro Lancaster was to sink the German battleship Tirpitz. The battleship had already come under attack on numerous occasions since October 1940 from Bomber Command, Royal Navy midet submarines and Fairey Barracudas of the Fleet Air Arm without success. Once again a Barnes Wallis designed bomb was used, this time the 12,000lb 'Tallboy', and No. 9 Squadron and No. 617 Squadron would be tasked with sinking the battleship. The first attack took place on the 15th September 1944 and scored one hit on the bow of the battleship making it unseaworthy. The second attack on the 29th October 1944 saw no direct hits but a near-miss did bend the ships propeller shaft. The third attack saw three direct hits and on the 12th November 1944 the Tirpitz was sunk.

As the war in Europe reached its conclusion the Lancaster would still take part in two more major operations. The first was 'Operation Manna' which lasted for nine days between the 29th April 1945 - 7th May 1945 which saw food dropped in Holland which had been in a famine since late 1944, during this operation a total of 3,156 sorties were carried out by the Lancaster. The second was 'Operation Exodus' which saw the Lancaster among a number of aircraft bringing home prisoners of war. It was also planned for twenty Lancaster squadrons to serve in the Pacific as part of the 'Tiger Force' in the run up to the invasion of Japan, 'Operation Downfall', but the war ended before this force was fully established.

Post-war use saw a number of Lancasters converted for civil use and re-named Lancastrian and four Mk B.IIIs were converted for the use of testing in-flight refuelling with two serving as tankers and two as the receiving aircraft. One of these flew non-stop from London to Bermuda, a total of 3,459 miles, and the two tankers also took part in the Berlin Airlift (1948 – 1949). The Lancaster was also to provide the base for its successor the Avro Lincoln and a number of aspects of the Lancaster were also used on the transport aircraft the Avro York.

The last Lancaster to roll of the production line was a Mk B.I, which from 1945 was re-designated B1, on the 2nd February 1946 it ended the production run of the type with 7,377 being built between 1941 - 1946. It would still be another 10 years before the type was withdrawn from Royal Air Force service, it also took part in the Berlin Airlift, when on the 15th October 1956 a Lancaster MR.3 from the School of Maritime Reconnaissance was retired, 15 years after the first prototype flight.