There was some Japanese fighter which had a gun installed behind the pilot pointing upward at a fixed 45 degree angle. It would drift in behind a flight of bombers above and let lose from below. Apparently, the bombers seldom knew from where the attack was coming until it was too late.
Germans used the same concept in their night fighters; usually pairs of cannon fixed to fire forward and up at 30 degrees. Took advantage of poor ventral defensive armament in British bombers. They called it Schrage Muzik (jazz, or literally “slanted” music).