Martin 250CE-17 upper turret
The PB4Y-2 was equipped with two Martin top turrets, designated as Martin 250CE-16 for the forward turret and 250CE-17 for the rear turret. These cylindrical-electrical turrets were located strategically along the aircraft’s fuselage to provide comprehensive defensive coverage.
Key Features of the Martin Top Turrets:
Location and Design:
- Forward Turret: Centered at station 3.0.
- Aft Turret: Centered between stations 5.3 and 5.4.
- Dome: The upper portion of each turret, protruding above the fuselage, was encased in a Plexiglas dome, offering an unobstructed view for the gunner.
Mechanics and Operation:
- Rotation: Capable of continuous 360-degree azimuth rotation.
- Elevation: Guns could elevate from -6.5 degrees to +85 degrees.
- Power: Driven by 24-volt electrical units, which managed the elevation, training, and firing of the weapons through electrical gears.
Construction:
- Turntable: The turret was built on an aluminum alloy casting weighing approximately 75 pounds. This casting housed the electric driving motor units, elevation drive torque tube, gun cradles, sight mounting yoke, gunner’s seat, control unit, supporting rollers, armor plate, Plexiglas enclosure, ammunition booster unit, and fire interrupter.
- Hoppers: Integral hoppers collected ejected cases and links, discharging them downward.
Fire Interruption Mechanism:
- Interrupter: Prevented the guns from firing when they were aligned with the aircraft’s tail structure. The interrupter used a cam system that replicated the silhouette of the PB4Y-2 in miniature. As the turret rotated, the cam turned and interacted with microswitches to halt gunfire when the aircraft’s structure came into the line of fire.
- Operation: The interrupter moved in sync with the gun’s elevation to maintain correct positioning, ensuring safety throughout turret movement.
Turret Rotation:
- Outer Ring: Acted as a track and contained a circular gear mated with the azimuth drive pinion. This mechanism enabled the complete turret assembly to rotate as a unit, including guns, ammunition, and gunner.
Armor and Protection:
- Armor Plate: Half-inch thick armor plate protected the midsection of the gunner, covering approximately a 30-degree angle in the direction of the guns. The lower armor plate also supported and protected the ammunition boxes.
Weight:
- Base Weight: Each turret weighed approximately 700 pounds, including all equipment but excluding the gunner and ammunition.
- Ammunition: With 800 rounds, the complete turret weighed around 940 pounds, adding 30 pounds for each 100 rounds of ammunition.
These turrets were designed to enhance the defensive capabilities of the PB4Y-2 by providing effective and flexible coverage against enemy attacks, ensuring the safety of the aircraft and its crew during missions.