Mk IB's were delivered to 19 Sqn in July 1940. The cannon were found to be so unreliable that these aircraft were eventually replaced by older ones from an OTU during the BoB.
By November 1940 the cannon were "fixed" and working properly, and IB's were re-issued to Fighter Command Squadrons.
The last 170 Spitfire Mk II's were Mk IIB with cannon.
Many Mk V's were converted from existing Mk I and II airframes, alot of these retained the 8x.303 armament("A wing") to become Mk VA's. Some VA's were built from new as well.
VB had 2x20mm and 4x.303 armament("B wing"), and the cannon were drum-fed with 60rpg.
VC introduced the so-called "universal wing". It was designed to be able to be fitted out with either "A wing", "B wing" or the new "C wing" armament(4x20mm). New belt-fed cannon meant they now had 120rpg instead of 60rpg.
Apparently there were 94 VA, 3,923 VB and 2,447 VC built.
There is a small issue with the AH Spitfire Mk V: It is a Mk VC since it has 120rpg for the 20mm, but graphically it has a Mk VB wing. The closed-off stubs for the uninstalled outer 20mm cannon are missing.
[This message has been edited by juzz (edited 11-10-2000).]