As originally conceived, destroyer escorts were to have the 5"/38 caliber gun as their main battery. Due to production shortages, the 3"/50 caliber (MK22) gun in on an open, pedestal-type, dual-purpose mount was substituted as the main battery armament. This gun was utilized in the first four classes of destroyer escorts. As production caught up with demand, the last two classes of destroyer escorts, the Rudderow and John C. Butler classes, were completed with 5"/38 caliber main batteries. the 3"/50 caliber gun was not nearly as effective as the 5"/38 caliber but provided a stop-gap weapon.
The gun is positioned by manually operated training and elevating gear. The elevation limits on the gun are approximately 13 degree depression and 85 degree elevation. Training stops are installed to prevent training the line of fire into the ship's superstructure. After the sights are set, the gun is positioned by the pointer and trainer bringing their telescopes on the target. The ammunition is hand loaded and hand rammed. The SLATER's guns used director control for more accurate firing.
The ammunition used in the 3"/50 caliber gun is the fixed type designed for an initial velocity of 2,700 feet per second. The maximum horizontal range is approximately 12,000 yards and the maximum ceiling range about 21,000 feet. The projectiles used in the 3"/50 caliber gun include: anti-aircraft, common, armor piercing and illuminating. These projectiles all weigh approximately 13 pounds, and the different types vary in length from about 9 to 13 inches.
A typical 3"/50 caliber mount is bolted to the deck and supports the roller-bearing paths and the training rack. The elevating and training hand wheel gear, seats for the pointer and trainer and platforms for the sight setter and checker are attached to the carriage. The gun recoils about 11 inches. The SLATER has MK21 mounts with fixed prism telescopes for the pointer, trainer and sight checker. These, along with auxiliary peep-and-ring type open sights, are mounted on a sight yoke supported by the slide. The sight-setting gear is on the left side of the gun abaft the pointers station and the sight checker is stationed on the right side near the trainer.
In their present configuration, the 3"/50 caliber guns on the SLATER have received a post-war modification to enable them to move automatically under the control of the gun director atop the superstructure. This modification was done while in Greek service and gives the gun a designation of MK26 Mod. 0.