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.
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.
[2] Following the formation of the Royal Air Force (RAF) 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 for their aero-engines.
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.
Sometimes, an alphabetic suffix was added to the mark number to indicate a minor change, e.g.: Bulldog Mk.IIA.
Otherwise, these two aircraft were identical in appearance and performance, and normally indistinguishable from each other but needed to be identified differently for maintenance.
Up until the end of 1942, the RAF always used Roman numerals for mark numbers, sometimes separated from its 'mark' abbreviation by a period (full stop).
For aircraft with a long service life, as their function evolves over time, the designation letters and sometimes the mark digit will change to reflect this.
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.
For example, the 'Fairey 6/22' was built to meet the 6th specification issued in the year 1922; it was subsequently accepted as the Fairey Flycatcher.