|The XV and 17
marks were reserved for the
naval version, the Seafire, in an effort to reconcile the
Spitfire numbering scheme with that of the Seafire.
The Mk. XVI was identical to the Mk. IX in all respects except for the engine, a Merlin 266. The Merlin 266 was a low-altitude version of the Merlin 66 and was built under license in the USA by the Packard Motor Company.