List of Air Ministry specifications

This is a partial list of the British Air Ministry (AM) specifications for aircraft. A specification stemmed from an Operational Requirement, abbreviated "OR", describing what the aircraft would be used for. This in turn led to the specification itself, e.g. a two-engined fighter with four machine guns. So for example, OR.40 for a heavy bomber led to Specification B.12/36. Aircraft manufacturers would be invited to present design proposals to the ministry, following which prototypes of one or more of the proposals might be ordered for evaluation. On very rare occasions, a manufacturer would design and build an aircraft using their own money as a "private venture" (PV). This would then be offered to the ministry for evaluation. The ministry may well release a specification based on the private venture aircraft if the plane aroused interest from the RAF or the ministry due to its performance or some other combination of features.

The system of producing aircraft to a specification ran from 1920 to 1949 during which the Air Ministry was replaced by first the Ministry of Aircraft Production (MAP) in 1940 and then the Ministry of Supply (MoS) in 1946. The system was applied to commercial aircraft as well, two being the de Havilland Comet and Vickers Viscount. During the period, over 800 specifications were issued.

Specification designations
Each specification name usually followed a pattern. A leading letter was usually present to identify the aircraft purpose. The codes used included B for "heavy bomber", e.g., B.12/36, P for "medium bomber", e.g., P.13/36, F for "fighter", e., F.10/35, and A for "army co-operation", e., A.39/34. The second part was a number identifying it in sequence and then after the slash, the year it was formulated, so in the example given above, B.12/36 signifies a specification for a heavy bomber, the twelfth specification of all types issued in 1936. Specifications were not always issued in sequence.

Admiralty specifications were identified by the letter N (Naval), e., N.21/45, and experimental specifications identified by the letter E (Experimental), e., E.28/39, with training aircraft signified by the letter T (Training), e., T.23/31, and unpowered aircraft, signified by the letter X, e., X.26/40. The letter G (General) signified a general-purpose aircraft, e.g., G.9/45, with an M (Multi-role) being applied to aircraft intended for more than one specific purpose, e.g., M.15/35.

The letter C (Cargo) was applied to military transport aircraft, e.g., C.1/42, with the letter O (Observation) used for a naval reconnaissance aircraft, e.g., O.8/38 – the letter S (Spotter) used for the more specialised role of naval spotting, i.e., observing and reporting back the fall of naval gunfire, e.g., S.38/34 – and R (Reconnaissance) for a reconnaissance type – often a flying boat, e.g., R.3/33. Special purpose aircraft would be signified by a letter Q, this being used to specify aircraft such as target-tugs, radio-controlled target drones, etc., e.g., Q.32/55.

Sometimes the purpose for which an aircraft is used in service would change from that for which the specification to which it was designed was issued, and so there are some discrepancies and inconsistencies in designation, the Royal Navy in particular liking to specify multiple roles for its aircraft in an attempt to make the best use of the necessarily limited hangar space onboard its aircraft carriers. In this case this resulted in several types designed to specifications originally intended to signify the naval Spotting role also being used for other purposes, e.g., S.15/33, resulting in the Blackburn Shark and Fairey Swordfish, the latter aircraft being primarily utilised as a torpedo bomber. Similarly S.24/37, which produced the Fairey Barracuda, again primarily designed for spotting, the dive bomber/torpedo bomber requirements being regarded as secondary when the specification was issued, but for which roles it was almost exclusively subsequently used, the original spotting requirement having been made obsolete with the introduction of radar.

In addition, some (mostly early) specifications appear to have no letter prefix at all, e.g., 1/21, the Vickers Virginia III.

List of specifications (incomplete)
The names of the aircraft shown in the table are not necessarily those they carried when provided for evaluation as at this point an aircraft would usually be referred to as the Manufacturer X.XX/XX, e.g., the Avro B.35/46 – this is in addition to the manufacturer's own separate internal designation for the aircraft, e.g., Avro 698. With several manufacturers submitting designs to the same specification this could result in a number of different aircraft with the same X.XX/XX designation, e.g., Handley Page B.35/46, etc. Upon acceptance of the design(s) the final service names would usually be chosen by the Air Ministry when they placed a production order, in the above B.35/46 cases, where two aircraft were accepted to this specification, Vulcan and Victor respectively.

Upon entering service, in the absence of any already-planned variants a new type would initially have no mark number after the aircraft name, being simply referred to as the Manufacturer Service-name, e.g., the Avro Anson, however upon acceptance of a new variant the previous (initial) version automatically became the 'Mark I', so in the example given, the previous (first) version of the Anson retrospectively became the Avro Anson Mk I upon acceptance of an Avro Anson Mk II. Sometimes planned variants would be later cancelled leading to 'missing' mark numbers, or the extent of the changes may have justified given the new variant a completely new name, e.g., the Hawker Typhoon II subsequently becoming the Hawker Tempest, or the Avro Lancaster B.IV & B.V entering service as the Avro Lincoln. In a few cases the same aircraft ordered with differing engines would be allocated separate names for each variant, e.g., Hawker Typhoon and Hawker Tornado, or the Handley Page Hampden and Handley Page Hereford. Typographical designation of mark numbers (Mk.) varied over time and inconsistencies are common, e.g., Mark II, ''Mk. II, II'', etc. Initially Roman numerals were used, changing to Arabic numerals post-World War II, e.g., Supermarine Spitfire Mk I to Supermarine Spitfire Mk 24.

Note 1: where possible mark numbers are given here in this list in the form that was used at the time of acceptance. Variations may be encountered due to changes in format/typographical convention.

Note 2: due to mergers and amalgamations within the UK aircraft industry sometimes the name of the manufacturer changed over time, e.g., English Electric later became part of the British Aircraft Corporation (BAC), so the English Electric Lightning then became the BAC Lightning; the British Aircraft Corporation itself and Hawker Siddeley (HS) then later merged and became British Aerospace, subsequently becoming BAe (now BAE Systems). Thus the previously mentioned Avro Vulcan was subsequently referred to as the Hawker Siddeley Vulcan; similarly, the Blackburn Buccaneer later became the Hawker Siddeley Buccaneer. Where possible, for clarity the aircraft in this list are listed under the ORIGINATING company's name or the name of the manufacturer under which it first entered production.

Specifications within the tables are listed in numerical order by year of issue; where a given number appears more than once, with one or more letter prefixes, the entries are presented in alphabetical order.

Air Board specifications (1917–1918)
In 1917, the Air Board began to issue specifications for new aircraft on behalf of the Royal Flying Corps and Royal Navy Air Service, with separate series for the RFC and Navy.

RAF specifications (1918–1920)

 * Data from: The British Aircraft Specifications File

1920–1929

 * Data from: The British Aircraft Specifications File