My guess is:
Consolidated PBY-5A Catalina aka "Black Cat"
It look that machine gun has night vision parts where the pilots and crews will be flying at the night for attacking Japanese Transport ships while the gunners have "night vision" parts against the enemy fighters at the night.
Otherwise, Matrin PBM-1 Mariner used to have 20mm on nose turret, but never came into operational during WWII and has 7 x 50 machine guns anyway.