Bomber Command is an organisational military unit, generally subordinate to the air force of a country. Many countries have a "Bomber Command", although the most famous ones were in Britain and the United States. A Bomber Command is generally used for strategic bombing (although at times, e.g. during the Normandy Landings, may be used for tactical bombing), and is composed of bombers (i.e. planes used to bomb targets).
RAF Bomber Command was formed in 1936 to be responsible for all bombing activities of the RAF. It found especial fame during World War II, when its aircraft were used for devastating night-time air raids on Germany and occupied Europe, principally the former, their bombing raids causing tremendous destruction of urban areas and factories.
Much of its personnel was drawn from outside the United Kingdom, many coming from the British Empire. Under the British Commonwealth Air Training Plan, many Commonwealth countries contributed squadrons or individuals to British air and ground staff. For example, No. 6 Group, which represented about one-sixth of Bomber Command's strength, was a Royal Canadian Air Force unit. Some non-British personnel came from occupied European countries.
At its height, Bomber Command under Air Chief Marshal Sir Arthur "Bomber" Harris could put over 1,000 aircraft into the air over Germany. Over 12,000 Bomber Command aircraft were shot down during World War II, and 55,500 aircrew were killed, the highest attrition rate of any British unit.