British military aircraft designation systems Since the end of the First World War , aircraft types in British military service have generally been known by a " type name " assigned by their manufacturer , or ( for various imported types ) bestowed upon them by the first military service to bring them into service . Individual variants are recognised by mark numbers . This is in contrast to the systems such as that used in the United States , where an aircraft type is primarily identified by an alphanumeric designation . Pre - 1918 . From about 1910 , the largest single designer of aircraft for the British Army ' s Royal Flying Corps was the Royal Aircraft Factory , Farnborough ( although most were built elsewhere ) . The Royal Aircraft Factory designated its types according to several categories , which were given the following prefixes : R . T . & T . E . were also used for strictly one off prototypes . The Admiralty chose to have private industry design and build its aircraft and frequently referred to designs by the serial of the first aircraft of that type to be accepted for service , although not always . The Army also bought industry - designed aircraft , especially when the Royal Aircraft Factory was unable to keep abreast of demand but no designation system was introduced during the war that covered more than the products of a single manufacturer . Specification numbers . 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 as by Manufacturer Name and Specification Number . If accepted they would get a service name . For example , the " Fairey 6 / 22 " ; this being the 6th specification issued in the year 1922 that was accepted as the " Fairey Flycatcher " . Later , a preceding letter was added to the Specification Number to identify the type of aircraft ; e . g . the " Bristol B . 28 / 35 " , a bomber aircraft , the 28th specification of the year 1935 , which would become the Bristol Blenheim . Naming . The names of aircraft would be suggested by the Air Ministry or Admiralty and agreed with the manufacturer when placing an order . Names generally followed one or a number of patterns ; Mark numbers . 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 " or " Mk . " ( e . g . Hawker 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 . Bristol Bulldog Mk . IIA ) . Occasionally , this letter indicated a change in role , e . g . the Bristol Blenheim Mk . I bomber was adapted to the Blenheim Mk . IF long - range fighter . 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 Boulton Paul Defiant Mk . I was adapted to a night fighter , the Defiant NF Mk . II , some of which were later converted to target tug s 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 form the Spitfire Mk . V ) . Series numbers . Occasionally other ' minor ' but nonetheless important changes might be denoted by Series numbers , preceded by " Series " or " Srs . " ( e . g . de Havilland Mosquito B Mk . IV Srs . I / B Mk . IV Srs . II ) . 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 Handley Page Halifax Mk . II Srs IA ) . Post - 1948 . In 1948 , Arabic numeral s replaced Roman numerals . This system has continued largely unchanged to this day with the addition of more prefixes as new roles have arisen . 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 use of the " Mark " or " Mk . " has gradually been dropped from use . 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 prefixed mark number can be presented in three different styles - for example : A full stop has generally been used to break the number from the prefix , e . g . C . Mk . 3 or C . 3 , a practice that has officially discontinued recently for current in - service types . 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 . Role prefixes . Role prefixes used at various times comprise :