gun synchronization to fire through propeller arc

[Graham Boak]

I suspect there were biplane fighters with 4 fuselage-mounted machine guns, although I can't think of one offhand. The Me 209-II had a similar wingroot mounting to the Fw series. The La 7 is nagging at me - there were versions with three cannon in the fuselage and others with either two or four. My books are temporarily out of reach.

Edit: the main advantage of fuselage mounting for the machine guns in the 1920s and 30s was the ease of clearing a jam. 1940s guns were more reliable, and multiple mountings were easier to design (and service) if in the wings. The increasing use of cannon meant fewer guns, but required greater space in the fuselage and wingroots which complicated the design. It was easier for Tank with a radial.

Possible a case could be made around the supposed German tendency of over-engineering for small benefit? However, Yakovlev was very vocal against putting guns in the wings, on agility grounds, so the size of the benefit can be argued.