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PROOF OF A SEVEN-INCH GUN AT MAXIMUM ANGLE OF ELEVATION, 40°, AT NEW LOWER STATION OF NAVAL PROVING GROUND.

[COPYRIGHTED]

U. S. NAVAL INSTITUTE, ANNAPOLIS, MD.

HOW THE NAVY DESIGNED AND BUILT THE
WORLD'S HEAVIEST FIELD PIECE

THE BUREAU OF ORDNANCE BRINGS OUT AN ENTIRELY
NOVEL TYPE OF MOUNT FOR A SEVEN-INCH
NAVY GUN FOR THE U. S. MARINES

By ENSIGN C. L. MCCREA, U. S. N. R. F.

Battleships of the Connecticut class when built were provided with a secondary battery of 7-inch 45-caliber guns mounted between decks. These seven-inch guns gave excellent service and were a good selection for the work that was expected of them, but had not been popular in the navy because they were too heavy for broadside work and too light for turret mounting, and a change was made in later battleships to the 5-inch 51-caliber guns, and then to 6-inch 53-caliber guns.

The experiences of torpedoed war vessels demonstrated the danger of having wide gun port openings in the broadside of vessels, such as the mounting of these 7-inch 45-caliber guns required in the Connecticut class. A heavy list from under water damage lowered the port sills to water, resulting in an inrush that capsized and sunk vessels that otherwise would have reached port. This being an undeniable fact, taught by bitter experience, the desirability of removing many of these guns and closing the ports when the battleships were assigned to convoy duty was self-evident. Therefore many of these guns were removed and thus became available for service elsewhere. The seven-inch guns removed may be described about as follows:

The gun with breech mechanism weighs 28,700 pounds, or about 14 tons. It is 45 calibers, 315 inches, or about 26 feet long, and gives a 153-pound shell a muzzle velocity of 2800 feet per second. At a range of 14,000 yards the shell has a remaining velocity of 1250 feet per second, and can penetrate several inches of armor

plate. Its maximum range at an elevation of 40° is in the neighborhood of 24,000 yards.

On board ship, the mount for the gun weighed nearly 30,000 pounds, so that the total weight of the gun and mount was not far from 30 tons. When the gun recoiled after firing, the maximum trunnion pressure exerted was about 195,000 pounds. A hydraulic brake took up the recoil through a distance of 21 inches, and the gun was brought back to battery or firing position in the usual way by means of heavy helical springs contained in spring cylinders attached to the slide in which the gun operated. The mount was designed to allow a maximum elevation of the gun of 15°, which allowed a range of about 14,000 yards.

The guns were too heavy for anti-submarine work on merchant ships, patrol vessels, etc., but for land use they were an excellent weapon. The urgent need of our forces in France for artillery was, of course, known, and a means for placing these guns into action in the war was earnestly sought.

Early application for a number of these guns was made by the U. S. Army, and a number were turned over. The guns thus turned over were mounted by the army on railway cars. Special cars were used for this purpose, built with a drop frame bed so that the entire seven-inch gun and its mount, exactly as it was used on board ship, could be placed on it and yet clear the French tunnel roofs and bridges when in transit, but none of these guns so mounted were sent abroad for service during the war.

This railroad mount was limited in its use by the fact that the elevation limit set by conditions on board ship was still maintained; that is, the gun was still capable of a maximum elevation of but 15° with its corresponding range of 14,000 yards. Further, the heavy trunnion pressures existing on account of the short length of recoil of the gun, while entirely satisfactory on board ship where the structure of the vessel is built to stand them, were troublesome when the mount was placed on a railway car. Strong outriggers and bracing of the car and bed were required when the gun fired at targets at an angle to the line of the track on which the gun car was located.

When considering the best way to place these guns in the war, the Navy Bureau of Ordnance first gave attention to the plan of mounting them on railway cars. They first set to work to increase the permissible angle of elevation from 15° to 30°, feeling that this was the minimum that should be allowed. The designs

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