United Kingdom military aircraft registration number, known as its serial number, or tail code is a specific aircraft registration scheme used to identify individual military aircraft in the United Kingdom (UK). All UK military aircraft are allocated and display a unique registration number. A unified registration number system, maintained initially by the Air Ministry (AM), and its successor the Air section of the Ministry of Defence, is used for aircraft operated by the Royal Air Force (RAF), Fleet Air Arm (FAA), and Army Air Corps (AAC). Military aircraft operated by government agencies and civilian contractors are also assigned registration numbers from this system.

An aircraft registration is a code unique to a single aircraft, required by international convention to be marked on the exterior of every civil aircraft. The registration indicates the aircraft's country of registration, and functions much like an automobile license plate or a ship registration. This code must also appear in its Certificate of Registration, issued by the relevant civil aviation authority (CAA). An aircraft can only have one registration, in one jurisdiction, though it is changeable over the life of the aircraft.