The Avro Lancaster is a British four-engined Second World War heavy bomber designed and built by Avro for the Royal Air Force (RAF). It first saw active service with RAF Bomber Command in 1942 and, as the strategic bombing offensive over Europe gathered momentum, it became the main heavy bomber used by the RAF, the RCAF, and squadrons from other Commonwealth and European countries serving within the RAF, overshadowing its close contemporaries the Handley Page Halifax and Short Stirling. The "Lanc", as it was affectionately known, thus became the most famous and most successful of the Second World War night bombers.