The Avro Lancaster was a four-engined, mid-wing heavy bomber designed and built primarily by the British company Avro (A.V. Roe and Company). Used by the RAF from 1942, along with the Handley Page Halifax, it was the primary strategic bomber of the RAF and other Commonwealth air forces. It was used primarily as a night bomber. The Lancaster, an evolution of the troublesome Avro Manchester, was designed by Roy Chadwick and was powered by four Rolls-Royce Merlin engines, or, in one version, Bristol Hercules engines. It entered service in 1942 and became the primary heavy bomber used by the RAF, the RCAF, and squadrons of other Commonwealth countries. The "Lanc", as it was affectionately known, became one of the most famous and successful aircraft of the Second World War, dropping 608,612 tons of bombs in 156,000 sorties and laying over 12,000 mines in enemy waters. In all, 7,378 Lancasters were built (excluding prototypes), 430 of which were in Canada, and 3,932 were lost in action. In addition to these, the aircraft derived from the Lancaster can be mentioned: the 202 Manchesters, the Lancastrian transports, the 253 York liners, the 604 Lincolns, which were the final derivative for bombing and the 185 Shackletons for maritime patrol.