Mk V (Types 331, 349 & 352)
Late in 1940, the RAF predicted that the advent of the pressurised Junkers Ju 86P bomber series over Britain would be the start of a new sustained high altitude bombing offensive by the Luftwaffe, in which case development was put in hand for a pressurised version of the Spitfire, with a new version of the Merlin (the Mk VI). It would take some time to develop the new fighter and an emergency stop-gap measure was needed as soon as possible: this was the Mk V.
The basic Mk V was a Mk I with the Merlin 45 series engine. This engine delivered 1,440 hp (1,074 kW) at take-off, and incorporated a new single-speed single-stage supercharger design. Improvements to the carburettor also allowed the Spitfire to use zero gravity manoeuvres without any problems with fuel flow. Several Mk I and Mk II airframes were converted to Mk V standard by Supermarine and started equipping fighter units from early 1941. The majority of the Mk Vs were built at Castle Bromwich.
Three versions of the Mk V were produced, with several sub-series:
Read more about this topic: Supermarine Spitfire (early Merlin Powered Variants), Single-Stage Merlin Engine Variants