I'll get back to you with a specific source.
LOL no need. I have all the Spit resources. Trust me on this one. I've been a Spit fanatic since the late 70s. I'm telling you, without a doubt that the Spit XVI did not carry 4 cannons.
There was one ground attack squadron in Italy, flying Spitfire Vc with 4 cannon, and they also had the large tropical filter under the nose. They were ground attack, not air to air.
The Malta Spit Vc that were delivered by carrier launched with 4 cannon but had 2 removed as soon as they got to Malta. The performance loss was not worth the extra 2 cannon. As was said at the time, if you can't hit em with 2 cannon, 4 isn't going to do you any good. Again, these Spit Vc had the large tropical filter which stole performance as well. The pilots wanted them lighter and better performing, not heavier.
No one was field modding 4 cannons, outside of one Spitfire VIII in the RAAF that was used to go after high alt Dinah recce birds.
The Spitfire 21, 22 and 24 had 4 cannons. The 22 and 24 did not see combat. The 21 was with 91 squadron in the late Spring of 45 before the end of the war but did not encounter any aircraft. Those Spits had completely redesigned wings.
Again, understand that the E wing, used by the Spitfire XVI was not equipped to handle 4 cannons. It was built to hold 2 cannon and 2 50s.
The Universal wing of the Spitfire Vc, the VII, VIII XII, part of the IX and XIV production runs could carry 4 but because of heating issues on the outer gun bay, it was not carried.
