User:Angusmclellan/spec p1336
P.13/36 was an Air Ministry Specification for a high-speed medium bomber aircraft for the Royal Air Force. It produced the Handley Page Halifax and, via the unsuccessful Avro Manchester, the Avro Lancaster bombers, two aircraft which equipped the main force of the Royal Air Force's Bomber Command in the latter years of the Second World War. The last aircraft which could trace their origins to this specification, Avro Shackleton airborne early warning aircraft, were retired in 1990.