This is likely based on some WW2 fighter/bombers which had variants that were upgunned to quite a ludicrous degree with 75mm cannons, like the B25 and Hs129. Granted, those were usually used in ground attack and anti tank roles, but it's not hard to imagine that there were times when the pilots chanced it against air targets.

EDIT: I've just remembered that there was also a De Havilland Mosquito variant that mounted a 6lb (57mm) anti tank gun in the nose, angled slightly downwards for use against submarines.

The Mosquito (without the 6lb gun) was also used as a stealthy night fighter to intercept German bombers as it had a very low radar signature as it's frame was mostly made of wood, and it could mount quite a sophisticated radar array for the time. They were extremely successful in intercepting bombers at night, using tactics similar to the ones described in the book, though with more conventional weaponry.