British WW2 heavy bomber designed by Roy Chadwick and built by Avro in the UK, as well as under license in Canada (Mk X). It evolved out of Chadwicks earlier design, the Avro Manchester, which was universally hated by all who were condemned to fly it, due to poor engine design. When Chadwick was able to get hold of 4 precious Rolls-Royce Merlin V-12 engines, he put them on the Manchester, lengthened the wings, and a legend was born.
The Lancaster was the mainstay of RAF Bomber Command from 1942 onwards, and was used for a variety of specialist tasks such as attacking the Ruhr Dams and sinking the Tirpitz. Its main role however, was in the great Area Raids which laid waste to many German cities by night whilst the Americans attacked by day.
It was the most effective bomb hauler in the Allies European Arsenal (the Boeing B-29 Superfortress could carry a larger bomb load, but was only employed in the Pacific against Japan towards the end of the War), and could carry almost twice the load of its US counterparts in Europe, these being the Boeing B-17 Flying Fortress and the Consolidated B-24 Liberator bombers.
Approximately 7000 Lancasters were built, of which roughly 4000 were lost on operational service, i.e. shot down by enemy night-fighters, anti-aircraft fire, or crashes.
Although controversy still rages over the employment of the Lancaster during the Strategic Air Offensive against Germany (Lancasters were the only bombers used by the RAF for the Dresden Raid of 13/14 Feb 1945 for example), there is little dispute that it was one of the greatest aircraft designs of the Second World War.
Some good reference material:
1. 'Night Bombers', Documentary DVD. Rare colour footage of Wartime Bomber Station in England, lots of Lancaster bomber stuff!
2. 'Enemy Coast Ahead', by W/Cdr Guy Gibson, VC, DSO/Bar,DFC (he was the leader of the famous 'Dambuster' raid, he was killed in action just after he wrote this book)
3. 'Dambusters' by Paul Brickhill (Peter Jackson is remaking the original movie from the 1950's)