Another significant difference between British and American Bombers was that the Single Pilot in a British Bomber was quite often a 19 year old Sergeant Pilot,indeed the whole crew was often Sgt Aircrew.
In American Bombers it was the norm that Pilots/Navs/Bombardiers were usually commissioned.Although slightly later in the war I believe some Bombardiers were initially given the Rank of 'Flight Officer' (like U.S Glider Pilots).And of course eventually it was realised that they did not really need all those highly trained Bombardiers and their role was often performed by 'Toggliers' (often an armourer or gunner ?) who toggled the bombs away when formation leads dropped,of course formation leads/deputy leads still needed a 'proper' Bombardier .