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