Aircraft Designations, United Kingdom

Since 1932, the Royal Air Force (RAF) and the Fleet Air Arm (FAA) have followed a designation system which was based on names assigned by their manufacturer. It was the only system used by the major combatants in which there was no alphanumeric system but rather, aircraft were directly known by their official names. At the beginning of the war, RAF aircraft were known by their name followed by a mark number written in roman numerals. Therefore, the first version of the famous Spitfire would be designated Spitfire Mk I. However, the system was flawed in that many structural changes applied to aircraft were left out and as a result, Spitfires could feature clipped wings or bubble canopies and would still be referred to by the same mark number. Armament changes nevertheless did merit a new designation, this was applied as a lower-case letter appended to the mark number. For example, the Spitfire Mk Ia included a slightly different armament set than that of the Mk I. There appear to be inconsistencies in whether the armament suffix was in uppercase or lowercase. Lowercase is used on this site in order to differentiate from a functional suffix which are in uppercase.

As the war progressed, many aircraft began to be utilized for different roles and it therefore became necessary to apply functional designations for these different variants. Below is a list of these functions, many of which were added as the war progressed and in the post-war era. In some early examples of multi-role aircraft, they were added as a suffix to the mark number. Thus the Coastal Command and fighter versions of the Beautfighter Mk. VI were known as the Mk VIC and Mk VIF respectively. This practice was discontinued quickly and replaced by one in which the functional designator was applied as a prefix to the mark number so, for example, the Beaufighter TF.Mk X was the strike fighter version of the Beaufighter. It was not uncommon for the "Mk" prefix to be omitted so that this same variant could be known simply as the TF.X (this standard is used throughout this site). After 1944, many aircraft were well into the teens or above in the number of marks and therefore, the clunky roman numerals after XX were replaced by Arabic numerals following the function prefix. For example, the twenty-first mark of the Spitfire was not known as the Mk XXI but rather as the Spitfire F.21. All British aircraft designed after the war have used Arabic numerals and function prefixes although old aircraft are almost always still referred to by their old roman numeral designations. It is also worth mentioning that marks are never repeated between different function variants of a same aircraft model. For example, the Hercules C.1 aircraft was followed in the transport role by the C.3 because a weather aircraft variant, the W.2 had the second mark already assigned.

The naming system for British aircraft followed a specific system based on branch of service (RAF or FAA) and function. Alliteration of aircraft name and manufacturer was very often applied, this practice had been obligatory between 1918-1921 and made voluntary afterwards. The FAA frequently assigned the "Sea" prefix to aircraft which had been designed initially for land-based operations. Thus, the naval variant of the Gladiator was known as the Sea Gladiator.