Since the end of the First World War, aircraft types in British military service have generally been known by a service name (e.g. "Spitfire"), with individual variants recognised by mark numbers often in combination with a letter to indicate the role. This is in contrast to identification systems used in countries such as the United States, where an aircraft type is primarily identified by an alphanumeric designation.
The British military aircraft designations (e.g. "Spitfire Mark V" or "Hercules C3") should not be confused with the serial number used to identify individual aircraft (e.g. "XR220"), nor with U.S. aircraft designations (e.g. "C-5", "C-17", "MQ-9") or manufacturer's designations (e.g. "Sikorsky S-58", "Jaguar B", "WS-61", "AW139", "WAH-64"), though Mark numbers were used to indicate aircraft built for other nations e.g. Hawker Hunter Mk 58 was a Hunter F.6 for the Swiss Air Force.
No designation system was introduced during World War I that covered more than the products of a single manufacturer. The Admiralty frequently referred to designs by the serial of the first aircraft of that type to be accepted for service.
In this system, which has been used since the end of World War I, each aircraft designation consists of a name, (sometimes) a role prefix and a mark number.
A unified official naming system was introduced in February 1918 by the Ministry of Munitions, the scheme would use classes of names related to the role. Fighter aircraft were to be animals, plants or minerals, bomber aircraft were to have geographical names and "heavy armoured machines" would be personal names from Mythology. The classes were further divided by size of aircraft and land or sea-based, for example a three-seater sea-based fighter would be named after shellfish. Italian towns were to be used for single-seat land-based bombers.
Following the formation of the Royal Air Force in April 1918 the Ministry of Munitions introduced a new system as Technical Department Instruction 538. They mainly followed the February 1918 scheme but certain names already used for engines were excluded, for example birds of prey were used by Rolls-Royce Ltd. The names related to zoology, geography and mythology were withdrawn in 1927 and the Air Ministry introduced names with the initial letters relating to role, for example "C" for troop carriers as used by the Handley Page Clive. A further change was made in 1932 and 1939 to use more appropriate names. Fighters were to use "General words indicating speed, activity or aggressiveness" and trainer would be "words indicationg tuition and places of education".
Bombers were to be named after inland towns in the British Empire, for example the Avro Lancaster and Fairey Battle (after Battle, East Sussex, the site of the Battle of Hastings). With the introduction of helicopters these were to be named after trees but only the Bristol Sycamore was named in this scheme.
The name ("type name") of an aircraft type would be agreed between the Air Ministry or Admiralty and the manufacturer/importer when the order was placed. Names generally followed one or a number of patterns:
The systems began to change in the immediate post-Second World War period with the V bombers and types such as the Supermarine Scimitar. The RAF's three post-war jet-engined, swept wing strategic bombers were given names beginning with "V" – Vickers Valiant, Avro Vulcan and Handley Page Victor (the V bombers).
Role prefixes used at various times comprise:
|A||Airborne (paratroop transport)||Halifax A.VII|
|AEW||Airborne early warning||Sentry AEW.1|
|AH||Army helicopter||Lynx AH.7|
|AL||Army liaison||Islander AL.1|
|AOP||Airborne observation post||Auster AOP.9|
|ASR||Air-sea rescue||Sea Otter ASR.II|
|ASaC||Airborne Surveillance and Control||Sea King ASaC.7|
|B(I)||Bomber interdictor||Canberra B(I).8|
|B(PR)||Bomber/Photo Reconnaissance||Valiant B(PR).1|
|CC||Communications transport||BAe 125 CC.3|
|COD||Courier – later Carrier – On-board Delivery||Gannet COD.4|
|D||Drone (pilotless aircraft)||Shelduck D.1|
|DW||Mine Exploding ("Directional Wireless")||Wellington DW.1|
|E||Electronics (particularly Electronic Warfare)||Canberra E.15|
|ECM||Electronic Counter-Measures||Avenger ECM.6|
|FA||Fighter/Attack||Sea Harrier FA.2|
|FAW||Fighter, All-Weather||Javelin FAW.9|
|FB||Fighter-Bomber||Sea Fury FB.11|
|FG||Fighter/Ground attack||Phantom FG.1|
|FGA||Fighter/Ground Attack||Hunter FGA.9 – (superseded by FG)|
|FGR||Fighter/Ground attack/Reconnaissance||Phantom FGR.2|
|FRS||Fighter/Reconnaissance/Strike||Sea Harrier FRS.1|
|GA||Ground Attack||Hunter GA.11|
|GR||General Reconnaissance (superseded by MR)||Lancaster GR.III|
|GR||Ground attack/Reconnaissance||Harrier GR.9|
|HAR||Helicopter, Air Rescue||Sea King HAR.3|
|HAS||Helicopter, Anti-Submarine||Sea King HAS.2|
|HC||Helicopter, Cargo||Chinook HC.2|
|HCC||Helicopter, Communications||Squirrel HCC.1|
|HF||High-altitude fighter (Spitfire only)||Spitfire HF.VII|
|HM||Helicopter, maritime||Merlin HM.1|
|HMA||Helicopter, maritime attack||Lynx HMA.8|
|HR||Helicopter, Rescue||Dragonfly HR.5|
|HT||Helicopter, Training||Griffin HT.1|
|HU||Helicopter, Utility||Sea King HU.4|
|KC||Tanker / Cargo||TriStar KC.1|
|L||Low-altitude fighter (Seafire only)||Seafire L.III|
|LF||Low-altitude fighter (Spitfire only)||Spitfire LF.XVI|
|Met||Meteorological reconnaissance (superseded by W)||Hastings Met.1|
|MR||Maritime Reconnaissance||Nimrod MR.2|
|MRA||Maritime Reconnaissance and Attack||Nimrod MRA.4|
|NF||Night Fighter||Venom NF.2|
|PR||Photographic Reconnaissance||Canberra PR.9|
|RG||Reconnaissance/Ground attack||Protector RG.1 expected in service 2024|
|S||Strike (nuclear capability)||Buccaneer S.2|
|SR||Strategic Reconnaissance||Victor SR.2|
|TF||Torpedo Fighter||Beaufighter TF.X|
|TR||Torpedo / Reconnaissance||Sea Mosquito TR.33|
|TT||Target tug||Canberra TT.18|
|TX||Training glider||Cadet TX.3|
|U||Drone (pilotless aircraft) – (superseded by D)||Meteor U.15|
|W||Weather research||Hercules W.2|
Starting in the interwar period, variants of each operational type were usually indicated by a mark number, a Roman numeral added to the type name, usually preceded by "Mark", "Mk." or "Mk" (e.g. Fury Mk I). Mark numbers were allocated sequentially to each new variant, the new mark number signifying a 'major' change such as a new engine-type. Sometimes an alphabetic suffix was added to the mark number to indicate a minor change (e.g. Bulldog Mk IIA). Occasionally, this letter indicated a change in role, e.g. the Blenheim Mk I bomber was adapted to the Blenheim Mk IF long-range fighter. Sometimes a minor but otherwise significant change in an aircraft would necessitate a new mark number, e.g., when the Lancaster I was fitted with Packard-built Merlin engines, which used a different make of carburettor from the Rolls-Royce-built ones, the Lancaster I became a Lancaster III. Otherwise, these two aircraft were identical in appearance and performance and normally indistinguishable from each other but needed to be identified differently for maintenance.
During the Second World War, as aircraft ordered for one purpose became adapted to a multitude of roles, mark numbers became prefixed with letters to indicate the role of that variant. Aircraft of the same mark that were adapted for different purpose would then be differentiated by the prefix. For instance the Defiant Mk I was adapted to a night fighter, the Defiant NF Mk II, some of which were later converted to target tugs as the Defiant TT Mk II. Where there was a Sea- variant, this would have its own series of mark numbers (e.g. the Seafire Mk I was derived from the Spitfire Mk V).
Occasionally other 'minor' but nonetheless important changes might be denoted by series numbers, preceded by "Series", "Srs." or "Srs" (e.g. Mosquito B Mk IV Series I / B Mk IV Series II – the different series number denoting the introduction, after a few initial production aircraft, of extended engine nacelles to eliminate buffeting. This design change was made standard on all subsequent production Mosquitoes). The series number denoted a revision during the production run of a particular Mark. This again could then have an additional letter-suffix (e.g. the Halifax Mk II Series IA).
Export variants of British military aircraft are usually allocated mark numbers (sometimes without a role prefix) from a higher range of numbers, usually starting at Mark 50. A converse convention was adopted for the Canadian-designed de Havilland Canada DHC-1 Chipmunk, where the sole British service variant was designated Chipmunk T.10.
Up until the end of 1942, the RAF always used Roman numerals for mark numbers. 1943–1948 was a transition period during which new aircraft entering service were given Arabic numerals for mark numbers but older aircraft retained their Roman numerals. From 1948 onwards, Arabic numerals were used exclusively. Thus, the Spitfire PR Mk XIX became the PR Mk 19 after 1948. With this change, the Sea- variants were allocated their own range within one common series for all variants (e.g. the Hawker Fury Mk I was followed by the Sea Fury F.10, Sea Fury FB.11 etc.).
The system has been largely unchanged since 1948 with the addition of more prefixes as new roles have arisen.
For example, the first Lockheed Hercules variant in RAF service was the Hercules C.1 ("Cargo, Mark 1"). A single example was adapted for weather monitoring purposes and became the Hercules W.2. The stretched variant became the Hercules C.3. With aircraft with a long service life, as their function changes over time, the designation letters and sometimes the mark digit will change to reflect this. The practice of restarting the mark numbers for the naval variant where the name was changed continued – e.g. the naval version of the Harrier, the Sea Harrier, marks started again at FRS Mk 1 – whilst variants where the name was unchanged for the naval version such as the Lynx have a single set of numbers for both land and naval variants. In the case of the Sea King, which began as a naval aircraft, the RAF kept the name and it also has a single set of numbers.
The post-1948 mark numbers are variously presented in full (e.g. Hercules C Mk 3) or abbreviated (e.g. Hercules C3) forms, and either with or without a full stop between the prefix and mark number. The use of the "Mark" or "Mk." has gradually been dropped.
From 1920 to 1949, most aircraft had an associated Air Ministry specification number. Prototype aircraft would be produced under contract and would be referred to by Manufacturer Name and Specification Number. If accepted they would get a service name. For example, the "Fairey 6/22" was built to meet the 6th specification issued in the year 1922; it was accepted as the Fairey Flycatcher. Later, a preceding letter was added to the Specification Number to identify the type of aircraft; e.g. specification B.28/35 for a bomber was the 28th specification issued in 1935; in this case the specification was specifically written for the Bristol 142M, a modification of Bristol's Type 142 private venture civil aircraft (Britain First) for military use as a bomber, which would enter service as the Bristol Blenheim Mk 1 light bomber.
From about 1910, the largest single designer of aircraft for the British Army's Royal Flying Corps was the Royal Aircraft Factory. The Royal Aircraft Factory designated its types according to either the layout of the aircraft or its role – e.g. Royal Aircraft Factory S.E.5, the "S.E." prefix representing Scouting Experimental. In practice successful Royal Aircraft factory designs were largely built by other manufacturers though still known by the Factory designations
Some examples of manufacturers designations and the corresponding service designations are shown below:
For some aircraft types (e.g. the C-17 which is currently known in RAF service as the "C-17 Globemaster III" ) the UK armed services have used the US designation rather than assigning their own designation.