Illustrations and performance details of the Erco 250SH Ball Turret mounted in the PB4Y Privateer from Aircrewman’s Gunnery Manual, Aviation Training Division, Office of the Chief of Naval Operations, U.S. Navy, 1944.
Erco Ball Turret
ERCO 250SH-2, 2A or 3The Erco Ball Turret is the bow installation in the Navy PB4Y-1 and PB4Y-2 airplanes. It serves a double purpose in taking care of any bow attacks on the Liberator besides being used for strafing, in anti-submarine warfare. Inasmuch as this turret is of the ball type, the gunner moves with his guns and sight in elevation and azimuth as he moves his control handles. It is a relative of the Martin 250SH Bow Turret of the PBM-3 airplanes and has many points of similarity in design and action.
There are several models which for the most part are the same—the Erco 250SH-2 or 2A used in the bow position of the PB4Y-1 airplane and the Erco 250SH-3 used in PB4Y-2 airplane.
Facts and FiguresPOWER: The Erco 250SH operates hydraulically on pressure built up by a hydraulic pump driven by a constant speed electric motor.
SIGHT: Its sight is the standard Navy Mk 9 reflector sight, fully described in the introduction of this section.
ELEVATION: From the horizontal position the turret ball, and consequently the guns, may be depressed a maximum of 70° and elevated a maximum of 85°.
AZIMUTH: This type of turret is capable of revolving 360° in azimuth, but for the installation in the bow of the PB4Y-1 or PB4Y-2 airplanes, its motion is restricted to 80° either side of the center line of the plane.
ARMOR: The armor plate of the turret consists of three parts to protect the gunner from enemy fire and flak: (1) 1½” laminated bullet proof glass to protect his face. (2) ½” armor plate in front to protect the gunner’s body, no matter where his guns are pointed. (3) ¼” armor plate bolted to the floor to protect his feet.
STOWING: The stowing position is 0° azimuth and 0° elevation, guns pointing straight forward.
