6"/47 Gun

Chapter X

a. Introduction

The only 6"/47 caliber gun installed on combat ships during world War II was the 6"/47 triple turret used by the light cruisers as the main battery for surface fire. There were no major design changes in this turret during the war.

The most significant development in this caliber was the design of the 6"/47 dual purpose twin mount. Initiated prior to the beginning of hostilities, it was still incomplete at the time of the Japanese surrender. However, it was estimated that the guns would be ready for installation on ships of the CL 144 class prior to their commissioning in December 1946.

b. History of 6"/47 Dual Purpose Twin Mount

In September of 1937 the first preliminary plans were submitted on the 6"/47 caliber twin double purpose turret. Considerable interest was evidenced in ordnance circles because it was the first attempt at automatic loading of a major caliber gun. Preliminary plans called for installation of this type of turret on the CL 55 class cruisers, with four turrets



per ship. Each turret was to contain two guns capable of 8° elevation and 5° depression. Two projectile hoists and one powder hoist were provided for each gun to Insure an available supply of either surface or antiaircraft ammunition . The expected rate of fire was 12 rounds per minute at all angles of elevation. The rate of elevation was to be 15° per second and train was to be 25° per second. The leading of the guns as first approved was by manual means with a lug type mechanical time fuze for antiaircraft projectiles. The mechanical time fuze projectile, after loading into the projectile tray, had to be aligned as closely as possible with the slots in the fuze setting head, an operation which slowed down the rate of fire. The fuze setting was to be automatic with a fuze setting regulator mounted on the gun slide. The projectile hoists were of the reciprocating non-reversible rack oar type with a designed rate of delivery of 15 projectiles per minute. The powder hoists were completely automatic, reversible, and of the dredger type.



At the time of the design of the 6"/47 dual purpose twin, international treaties on weight limitations restricted the use of these turrets to vessels of the GL55 class. From 1937 until 1943, work was practically suspended on the 6"/47 dual purpose twin, because of pressure of other activities in the Bureau which had higher priority. In August 1943, Admiral King recommended that design of the proposed light cruiser carrying 6" double purpose guns proceed without delay. This action was approved by the Secretary of the Navy on August 26, 1943- Characteristics set up by the General Board pertaining to turrets were:

"Guns; Twelve 6"/47 caliber double purpose guns mounted in six turrets on the centerline, three forward and three aft, as completely mechanized as possible, arranged with special attention to volume of high angles of fire in all directions."[1] It was decided that the new design would be used in cruisers CL144 to 147 inclusive, all to be built by the New York Shipbuilding Corporation.



In the fall of 1943, complete general arrangement sketches of the slides and turrets were forwarded to the Naval Gun Factory. These were for information in the detailing and manufacture of equipment and the construction of a wooden mock-up. For improved ballistics of antiaircraft fire, the Army slotted-type fuze M43 was adopted since it was more accurate and cheaper than corresponding Navy fuzes. It required a projectile which was longer and of a different contour than one having the M18 fuze. The length of the new antiaircraft projectile was increased from 26.7 to approximately 30.0 and weighed about 105 pounds. The increase in length made it necessary to redesign the fuze setting and loading mechanisms and to increase the slide working radius. To simplify the design of the loading mechanism the illuminating projectile had been increased to the same length as the antiaircraft projectile. The new fuze setter as capable of correctly setting the fuze without regard to the relation of the fuze on the projectile or the setting pawls in the fuze setter.



The general arrangement plans for the powder and projectile hoists were drawn up by the Bureau of Ordnance and detailed drawings from these plans were made by the Hock Island Arsenal, Rock Island, Illinois. Pilot models were manufactured by the Jeffrey Manufacturing Company, Columbus, Ohio, and the production hoists were manufactured, assembled, and tested by Norberg Manufacturing Company, Milwaukee, Wisconsin. Hydraulic equipment was developed and furnished by Vickers Incorporated, Detroit, Michigan. The original plans submitted to the Naval Gun Factory called for manual loading operation of both the projectiles and powder cases. As the result of loading drills held on the mock-up and observed by the Chief of the Bureau of Ordnance and officers from the Special Ordnance Board, recommendations were made to change the design so that less manual labor was required in the loading operations. Projectile loading was improved by the adoption of a loading shelf, on which the projectiles were slid from the hoist to the loading tray — the front end of the projectile being tilted to coincide with the angle of elevation of the gun — then pushed into the tray. Powder handling was improved by the addi-



tion of a manually operated powder cradle which eliminated the transfer of the powder case from the hoist to the slide. However, tests proved that manual operation of the powder cradle was too laborious and the design accordingly was modified to include fully automatic electric hydraulic operation. In this way, the powder case loader was eliminated.

Functional schematic diagrams of electric hydraulic equipment for slide, housing rammer, and breech mechanism were developed by the Bureau of Ordnance. The contract for the manufacture of this equipment was let to Vickers Incorporated, Detroit, Michigan.

Detailed drawings of slides and girders were made at the Naval Gun Factory which also manufactured the slides. In March 1944 two experimental slides and a proving ground girder were manufactured and assembled by the Naval Gun Factory In order to prove and test loading mechanisms. A special emplacement at the Naval Proving Ground was also provided to mount the girder and proof fire the gun. For purpose of comparison the first slide included a hydraulic



breech mechanism and the second, a mechanical hydraulic type breech mechanism. Difficulties encountered by the manufacture of the control cams and valves to meet the expected time cycles led the Bureau to accept a slightly lower rate of fire so that testing could be expedited. Valuable experience was gained for future application, since the mechanisms involved were the first of their kind. Production design for shipboard installation was changed to correct the slight faults discovered in proof firing tests and a rate of fire exceeding the desired rate by approximately 2 R.P.M. per gun was accomplished. To conserve weight, the pedestal block and counterweights were removed from the slide, which brought the balance of the slide assembly within acceptable limits.

The original design of the projectile ring was very crude as it required that each projectile be lifted by manual labor, causing fatigue of crew and subsequent slowing of rate of fire. A thorough Investigation of this feature resulted In the perfection of a rotating ring which eliminated the lifting of projectiles.



In July 1942, it was decided to dispense with range finders in order to reduce the weight and clearance required for the turrets. Elimination of the range finders allowed an additional turret per ship if desired. Radar equipment was added to replace the range finders used as secondary control.

In August 1945 the Bureau of Ordnance decided to use one-man control for the turret and the driving of a lead computing sight.

In December 1945, it was recommended that electric primers be used because of doubt as to the safety of the percussion element of the 6"/47 caliber ammunition when used with a rammer speed of twenty feet per second.

By December 1945 design for all components of the 6"/47 dual purpose twin had been competed except for the gun loading circuit diagram and gun control (elevation and train). At this time, it was noted that because of the late scheduling of slides, the program would be delayed one month for the first ship and two months for the second. The pilot slide and hoist drives were demonstrated at the plant of Vickers Incorporated, on October 17, 1945. Certain modifications were deter-



mined to be necessary which resulted in the delay. Completion of the pilot turret was scheduled for June 1, 1946.

c. Plane for Proposed 6"/47 Twin Turret

During the war the need for an effective anti-aircraft screening vessel became apparent. Ships of the CL95 OAKLAND class were designed for this purpose but there were too few of them to be adequate. In May 1945 the Secretary of the Navy requested the General Board to study the desired characteristics of a CL/AA.[2] However, because it was considered improbable that guns would be made available to construct new antiaircraft vessels in time of peace, it was decided to modify cruisers of the CL55 and 64 classes for this purpose. Three ships of the CL55 CLEVELAND class were to be modified to serve as a prototype for future conversion to antiaircraft vessels. Plans called for a 6"/47 twin to replace the present 6"/47 triple turret on these vessels. The 6"/47 triple turret guns would elevate to 60° it was planned and were to be controlled in "AA fire"



by the main battery director. However, for AA fire an additional computer was required to provide the proper gun orders. The new twin design called for an elevation of at least 70° but preferably 85°. Ammunition handling methods would be semi-automatic with semifixed ammunition being fed into the gun from either side of the slide with a higher rate of fire than the CL114 class.

At the end of the war this gun was in the preliminary stages of development but indications pointed to its use for countering: atomic bomb or guided missile attacks by keeping the control planes distant from their target.

d. 6"/47 Triple Turret Production Program.

The 6"/47 triple turret gun program involved the procurement of 148 assemblies at a total approximate cost of $38,800,000.[3]

The Naval Gun Factory, with the exception of the powder and projectile hoists, was the sole source of supply for these turrets, because of its heavy production schedules, the job shop nature of its work, and the fact that the manufacture of turrets was not



easily adapted to mass production, many anxious moments arose during the early stages of the shipbuilding program. The Gun Factory, nevertheless, was able to ship the ordnance equipment to the shipbuilders within the time required for installation with the result that throughout the entire war period lack of turret equipment in no case caused delay in a ship's completion date.

The Jeffrey Manufacturing Company supplied all the powder and projectile hoists, and its performance was outstanding. Various other components were produced by commercial manufacturers. The Gilbert and Baker Manufacturing Company produced the sights, the elevating and training gun attachments as well as the fuze setters. Rammers were manufactured by the Carrier Corporation, which did an excellent Job on this particular work. General Mills machined counter-recoil cylinders and plungers.[4]

The Bethlehem Steel Company and the Midvale Company produced the 6"/47 forgings which were shipped to the Gun Factory and South Charleston for machining. Advanced deliveries permitted suspension of barrel



production in 1943.[5]

The procurement program for hydraulic equipment was initiated early in 1940 with the placing of contrasts for material for CLs 55-58. After December 7, 1941 procurement was increased to cover 41 vessels. Deliveries from the prime contractors--Arma, Northern Pump Company, Northern Ordnance Inc., and Vickers was very satisfactory. When V-J Day arrived all equipment and spares for the 41 vessels, with the exception of some elevation and train receiver regulators, had been delivered. The drives which were delivered for the eight vessels cancelled on V-J Day were turned over to the Maintenance Division for storage as spares and for possible future modernization use.[6]




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Transcribed and formatted by Thomas Wildenberg, HyperWar Foundation