4"/50 Mount Mark 12 Mods

Chapter VIII

a. Introduction

The 4"/50 caliber wet and dry-type mounts were installed on destroyers, auxiliaries, merchant vessels, and submarines. No new designs were developed during World War II. Several OrdAlts were issued to improve the operation of the mounts, one of which (Mo.661) provided an Improved type of foot-firing mechanism.

b. History and Characteristics

The 4"/50 caliber Mount Mark 12 was designed primarily for use on destroyers and embodied the features of the 5"/51 caliber broadside mount.[1] It had an angle of elevation of 20 degrees and a depression of 15 degrees. The trunnion height was 45 inches. On early mods the recoil was 27.5 Inches; redesign of the recoil spring wet mounts which were modifications of the dry mounts, provided corrosion-resistant plating and materials for the mechanism, and watertight covers for the muzzle and breech.



The muzzle velocity was 2900 feet per second the maximum range, 16,200 yards at 20 degrees elevation. The projectile weighed 33 pounds and used fixed ammunition.

The gun had a hand-operated, stepped screw-type breech plug. The mount had one hydraulic-type recoil cylinder and two spring-type counter recoil cylinders mounted on the under side of the slide.

c. Procurement

During the course of the war 143 of these 4"/50 wet-type mounts were procured at a cost of $4,290,000. When the program was first initiated, Walter Scott and Company were awarded a contract for 180 mounts. The Navy had on hand some 30 of the dry-type mounts which were converted toy the Naval Gun Factory. Production schedules on the 3"/50 and 4"/50 wet mounts were so arranged that as 3" production was reduced, the 4" took up the slack. The 4"/50 proved ineffectual in combat and before the original program was completed the Bureau switched to a 5"/25 caliber wet mount.


A total of 1204 of the dry-type mounts were procured, primarily for installation on merchant vessels.



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Transcribed and formatted by Thomas Wildenberg, HyperWar Foundation