The registry is organised by production series, because that is how Triumph built the car and how the numbering works. Live counts for each era are on the registry — this page is about what actually changed.
Mk1 — Spitfire 4, 1962
Giovanni Michelotti’s body over the Triumph Herald’s frame, drivetrain and independent rear suspension, powered by the Herald’s 1,147cc four. Roll-up windows in a class that mostly did without them, and a bonnet that hinges forward as one piece.
Mk2, 1965
Same silhouette and the same 1,147cc engine, with a warmer camshaft and a tidier interior. The commission-number sequence continues straight on from the Mk1 rather than restarting, so the number alone will not separate a late Mk1 from an early Mk2.
Mk3, 1967
The engine goes out to 1,296cc, and the front bumper is raised — the quickest visual identification of a Mk3 from the front, and a direct answer to US regulations.
MkIV, 1971
Michelotti back for a second pass: the tail is squared off, the interior substantially reworked, and — the change that mattered most — the rear suspension is redesigned to settle the swing-axle cornering behaviour the earlier cars were criticised for.
1500, 1973
The block is stroked to 1,493cc. North America gets the 1500 first, in 1973,
under its own FM numbering, while the rest of the world is still buying MkIVs;
rest-of-world 1500s continue the MkIV’s FH sequence from 1975. Emissions
equipment on US-market cars ate most of the power the extra capacity provided.
From October 1979 the last cars carry VINs rather than commission numbers. Production ended in 1981.