[rof120]

I don't think the LW bothered to change the type designation after the wings were changed to cannon wings but I can't be positive, I don't really know (what about the relevant Squadron/Signal description? My copy is not around right now.) I think the E-3 had a slightly more powerful engine (?) and possibly some more small modifications.

About the wings there is a famous exception: when Adolf Galland's E-4 was replaced by a F-2 or so he disliked the new armament mix with only two light machine-guns (7,92 mm) above the engine and a 15 mm, later 20 mm cannon (MG 151) firing through the propeller hub. He discussed this point in detail in his book "Die Ersten und die Letzten/Les premiers et les derniers /The First and the Last". According to him the light MGs had become useless "fireworks" because enemy AC were becoming tougher and tougher (with added armour plating etc., not to mention - later - B-17s and B-24s). So Galland, who was leading JG 26 (he was their Geschwaderkommodore so he was in a position to take such decisons), had the standard F-wings replaced by E-3 or E-4 wings on his two personal 109s for as long a time as possible (as long as such wings were available). There are some photographs, in particular shot during Göring's visit to Galland's JG 26 in November 1941.