however the Lincoln had more in common with the Manchester than the late models of Spitfire did with the early versions so it wasn't consistent. A trend might also be followed by a manufacturer – Hawker Hurricane, Typhoon, Tornado, Tempest. Where civilian aircraft types have been taken into service, their existing names or alphanumeric designations have often been retained, e.g. the Vickers VC10 or Lockheed TriStar. The systems began to change in the immediate post-Second World War period with the V bombers and types such as the Supermarine Scimitar. The RAF's three post-war jet-engined, swept wing strategic bombers were given names beginning with "V" – Vickers Valiant, Avro Vulcan and Handley Page Victor (the V bombers). Role prefixes Role prefixes used at various times comprise: 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", "Mk." or "Mk" (e.g. 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. Bulldog Mk IIA). Occasionally, this letter indicated a change in role, e.g. the Blenheim Mk I bomber was adapted to the Blenheim Mk IF long-range fighter. Sometimes a minor but otherwise significant change in an aircraft would necessitate a new mark number, e.g., when the Lancaster I was fitted with Packard-built Merlin engines, which used a different make of carburettor from the Rolls-Royce-built ones, the Lancaster I became a Lancaster III. Otherwise, these two aircraft were identical in appearance and performance and normally indistinguishable from each other but needed to be identified differently for maintenance. 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 Defiant Mk I was adapted to a night fighter, the Defiant NF Mk II, some of which were later converted to target tugs 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 from