The Lancaster was a development from the two-engined Manchester, which was always an unsatisfactory aircraft. The Manchester was a response to the air force’s obsession with twin-engined bombers in the 30s, which would have required engines of greater power than were available at the time, and led to a change in mindset due to the comparative success of our allies with four-engined bombers. Rather than start from scratch, AVRO simply re-designed the Manchester by adding an extra wing section between the inner engine and the outer, thereby extending the wing and improving both lift and power output substantially – of course it wasn’t that simple. AVRO’s chief designer, the incredible Roy Chadwick submitted this design to the specification that also brought forth the designs for the Halifax and the Stirling, in a sort-of prequel to the post-war V-bombers, where the Government gave the go-ahead for all three due to the untried technology being used. The use of the then-new Merlin engine with its previously unheard-of power output put the Lancaster’s various capabilities into alignment and created a rather impressive “heavy”. After renaming the initial prototype Manchester III to Lancaster perhaps to distance it from its less-than-stellar twin-engined sibling, the prototype first flew in 1941, partially due to the fact that AVRO had already been working on improving the performance of the Manchester, and partly because of the urgent need for a heavy bomber capable of taking the fight (and a lot of bombs) to Berlin. A large contract for over 1,000 Lancasters was soon forthcoming, and further production was begun at AVRO Canada after an airframe was flown to them as a pattern for production. The quality of the eventual design was such that very few noticeable differences were made between the initial and later variants, with cosmetic changes such as side windows and the enlarged bomb-aimer’s window being some of the few that were readily seen if we ignore the specials. The main wartime alternative to the B.I was the B.III, which differed mainly by having license-built engines that were manufactured in the US by Packard, with over 3,000 built. The installation was so close to the original, that a B.I could easily be retrofitted with a Packard built Merlin with very little problem. There were of course the “Specials” such as the Dambusters and Grandslam versions, but other than 300 or so of the Hercules radial engine Lancs, most of the in-service machines looked very similar.At the end of WWII the Lancaster carried on in service in some shape or form for long after hostilities ceased, with a name change to Lincoln when the design became mostly unrecognisable, and later the spirit of the original design lingering on in the Shackleton, which retired in the mid 1980s, 40 years after the end of WWII.