Instructions :
Activation group 1-2 for gun
And use vtol and trim to move gun

Wiki:
The Lockheed PV-1 was the designation given to the Ventura bomber in service with the US Navy. In the spring of 1942 the USAAF agreed to transfer responsibility for all anti-submarine warfare off the American coast to the US Navy, after years of fighting to keep that role. Part of this agreement saw responsibility for the Ventura pass from the USAAF, where it was designated as the B-34, to the US Navy. Eventually 2,162 aircraft were built with the PV designation (Patrol, Lockheed), of which 1,600 would be PV-1s.

A number of modifications were made to the Ventura to make it more suitable for the maritime patrol role. It retained the 2,000hp R-2800-31 engines used on the Ventura II, but fuel capacity was increased from 1,345 US gallons to 1,607 US gallons, half in permanent fuel tanks, 310 gallons in drop tanks and the rest in optional bomb-bay fuel tanks. The PV-1 was armed with two forward firing 0.50in guns, twin 0.50in guns in the dorsal turret and two 0.30in guns in the ventral position. The bomb bay was modified so that it could carry six 325lb depth charges, a single torpedo or the normal 3,000lb of bombs of the Ventura II.