British military aircraft designation systems

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:

• Alliteration was particularly common; e.g. aircraft from Vickers-Armstrongs were given names starting with V,[2] Hawker Aircraft, names starting with H, etc. This began during the First World War, when aircraft manufacturers were given an initial pairing of letters to use in the naming of their aircraft: e.g. Boulton Paul Ltd were given "Bo". From this and the requirement to use the names of birds or insect for fighter aircraft, their first in-house fighter design was the Boulton Paul Bobolink. For bombers the additional requirement was a placename, hence the Boulton Paul Bourges; and its contemporaries – the Airco Amiens and Vickers Vimy (Bourges, Amiens and Vimy all being in France).[3]
• Heavy bombers received the names of cities and towns – Short Stirling, Avro Lancaster, Handley Page Halifax. Likewise Transport aircraft also received the names of cities and towns – Avro York, Vickers Valetta, Handley Page Hastings, Blackburn Beverley.
• Flying boats were given the names of coastal or port communities – Saro London, Supermarine Stranraer, Short Sunderland.
• Land-based maritime patrol aircraft were named for naval explorers – Avro Anson (George Anson, 1st Baron Anson), Lockheed Hudson (Henry Hudson), Avro Shackleton (Ernest Shackleton), Bristol Beaufort (Francis Beaufort).
• Aircraft for army co-operation and liaison and gliders were given names associated with mythological or legendary leaders; e.g. Westland Lysander, Airspeed Horsa, General Aircraft Hamilcar, Slingsby Hengist. A sense of irony was present when some of the names were chosen as Hengist and Horsa were the mythical Germanic leaders in the invasions of the British Isles in the 5th century.
• American aircraft, whether purchased directly or sourced under Lend-Lease, were given American-themed names following established patterns, e.g. the Martin Baltimore, Consolidated Catalina. The American services, with the exception of the U.S. Navy, were not generally in the habit of giving aircraft names, and many British-chosen names would later be adopted; e.g. the North American P-51 Mustang began life as the North American Mustang Mk.I with the RAF. U.S. Navy names, conversely, were being increasingly adopted by the Fleet Air Arm as 1942 and 1943 progressed, as in the case of the Grumman F4F Wildcat shedding its alternative Fleet Air Arm "Martlet" name in favour of "Wildcat", the original American naval name.
• Naval versions of aircraft not originally ordered for the Fleet Air Arm were given the prefix "Sea" such as with the Hawker Sea Hurricane and de Havilland Sea Venom while Seafire for the navalised Supermarine Spitfire was a contraction of "Sea Spitfire". Sometimes the naval version entered service without a corresponding land-based type doing so, as with the Hawker Sea Fury and de Havilland Sea Vixen.
• Naval aircraft ordered as such had names with a nautical theme – e.g. Supermarine Walrus, Blackburn Roc, Fairey Gannet. Torpedo bombers were given 'fish' names, e.g., Blackburn Shark, Fairey Swordfish, Fairey Barracuda. Mythological names, particularly with an association with water were common, such as Blackburn Iris – named for the goddess of sea and sky, and Nimrod the mighty hunter, used for the Hawker Siddeley Nimrod and Hawker Nimrod. Nimrod aside, many naval fighters were named for birds – such as the Fairey Flycatcher, Fairey Fulmar, Blackburn Skua and, before the aforementioned adoption of the U.S. Navy's existing names for Fleet Air Arm aircraft of American origin, Grumman Martlet (the martlet being a heraldic bird) for the F4F fighter.
• Training aircraft were given names related to academic institutions – Airspeed Oxford, North American Harvard, Boulton Paul Balliol, Fairchild Cornell. As with other American aircraft purchased, appropriate US names were used – the Harvard and Cornell universities. Alternative names for teachers were also used – De Havilland Dominie, Percival Provost, Miles Magister, Percival Proctor.
• Aircraft built for one role such as the Avro Anson or Armstrong Whitworth Albemarle but converted to other roles rarely changed their names. However significant changes in a design might result in a name change – the Avro Manchester was renamed Avro Lancaster, which was in turn renamed Avro Lincoln as the design was improved, however the Lincoln had more in common with the Manchester than the late models of Spitfire did with the early versions so it wasn't consistent.
• A trend might also be followed by a manufacturer – Hawker Hurricane, Typhoon, Tornado, Tempest.
• Where civilian aircraft types have been taken into service, their existing names or alphanumeric designations have often been retained, e.g. the Vickers VC10 or Lockheed TriStar.

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:

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.[6] 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[7] (e.g. Hercules C Mk 3) or abbreviated[8] (e.g. Hercules C3) forms, and either with[9][10] 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:

Avro 549A = Aldershot II

Vickers VC10 Type 1180, the tenth "Vickers Civil" design, were (Type 1106) VC10 C1 transports converted to have additional tanker role; known in service as Vickers VC10 C1K

Westland WAH-64 Apache = Apache AH1

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.