You wrote MK IV where you mean MK IX. That was the Mark developed to fill in as the more advanced MK VIII was completed.
As it happened, MK IX was very well distributed, with the eventual MK VIII used primarily over Italy and in the Far East, where it was a very dangerous foe to the Japanese.
That's correct. I get a little dyslexic when I'm tired.
The only "Mk IV" Spitfire the PR Mk 1 Type D, which was a long range photo recon variant, with an integral leading edge wing tank, and (initially) a 29 gallon fuselage tank behind the pilot. Like the P-51 B through K variants that fuselage tank moved the center of gravity so far aft that the aircraft was difficult to maneuver safely until most of the fuel in it was used. Unlike the P-51, it was deleted from the later Type Ds, and the type was renamed the PR Mk IV. This also made sense as it had a Merlin 45 engine in it, like the Mk V.
The Mk VI and VII were high altitude fighters with pressurized cockpits. Both were based on the Mk V, with cockpit pressurization. The Mk VI was less developed interim design using a Merlin 47 with a single stage supercharger adapted for high altitude. The Mk VII, like the Mk VIII was intended as a high altitude replacement for the Mk V, and it used the same Merlin 61 as the interim Mk IX. However the Mk IX itself was nearly as capable as the Mk VII, so only 140 Mk VIIs were ever made. One of them was shipped directly to the US for evaluation purposes and now sits in the Smithsonian Air and Space Museum.
The Mk VIII was essentially a Merlin 61 powered Mk VII without the pressurized cockpit or extended wing tips (although there were also HF Mk VIIIs produced as well with the Merlin 70 and extended tips, as well as an LF variant with square tips and a Merlin 66).
The Mk VII and Mk VIII had a stronger fuselage than the MK V to accommodate the two stage supercharged Merlin 61. They also had a retractable tailwheel and a taller, pointed vertical stabilizer. The cut down rear fuselage was introduced during Mk VIII production, which then also appeared in the later Mk IX as well as on the Griffon powered Mk XIV.
The Mk XIV as in fact based on the late production Mk VIII fuselage further adapted for the larger and heavier Griffon engine.
Nearly all sources mention the A, B, C and E wings which differed primarily in their armament. The A wing had eight .303s, the B wing had two 20mm cannon with 60 rounds per gun, and four 303s, C wing or “universal” wing could take eight .303in machine guns, or four 20mm cannon, or two 20mm cannon with 120 rounds per gun and four machine guns, plus a 250 pound bomb under each wing, or a 500 pound bomb under the fuselage. The D wing as mentioned previously was intended for the long range PR variants, and as such had no armament and an integral leading edge wing tank. The E wing was a revised universal wing that carried two 20 mm cannon in each wing, mounted outboard rather than inboard as on the B and C wings, and also had two .50 caliber machine guns. The outboard cannon placement made more room for the .50 BMG ammunition, and also spread the stresses out over the wing better, separating the cannon from the underwing hard points for the bombs.
Nearly all sources also mention the Merlin and Griffon engine variants, but few mention the significant differences in supercharging for the L, F and HF variants, the use of single stage, two stage, and two stage-two speed superchargers on various engine marks, and the differences impeller sizes on superchargers designed for optimum performance at different altitudes, and most sources don't make the point that there were in essence only two major fuselage designs through out Spitfire production.
The also don't point out that from a pure handling perspective, the Mk V was arguably the sweet spot, with a near perfect blend of power and handling. The later Spitfires had more power and greater performance, but it came at the expense of greater weight and somewhat reduced maneuverability.
Most sources also do not directly state that the British did not regard airframes as throw away items, as did the US. Mk Is were reworked to Mk II status, many surviving Mk II airframes were reworked to Mk V status and many surviving Mk V airframes were reworked to Mk IX status, with a handful of Mk Vs being converted to Mk VI status. In other words, significant parts of a pre-war Mk I fuselage theoretically could have flown through the entire war with the fuselage being upgraded to Mk V and eventually Mk IX status, with a new C or E wing being installed in the Mk V or MK IX stage of the process. That just didn't happen in the US.
