Designed to meet a specification for a new generation of " worldwide use" medium bombers, the Avro Lancaster was first used on January 8, 1941. The Lancaster was based on a twin-engine aircraft named Manchester. The heavier Lancaster had four engines and a large bomb bay, later versions of which could carry 22,000 lbs bombs. Used primarily as a night bomber, the Lancaster was a versatile aircraft that became most famous for its role in the 1943 "Dam Buster" raids on the Ruhr Valley dams in Germany. Between 1942 and 1945, Lancasters flew 156,000 sorties, dropping 608,612 tons of bombs on enemy targets.