Designed to fulfill the needs of battleships as well as destroyers, the 5-inch/38-caliber dual-purpose gun became one of World War II’s best regarded and most versatile naval weapons. It was the conflict’s iconic U.S. destroyer gun as well as the Navy’s workhorse on board capital ships, cruisers, and auxiliaries. Many more 5-inch/38s were made than any other World War II medium-caliber naval gun.
In the 1920s, the Navy used different guns to deal with aircraft and with surface targets. U.S. battleships and some destroyers were armed with high-velocity 5-inch/51s (the second number refers the length of the barrel in multiples of caliber; in this case, 5-inch caliber x 51 = 255-inch barrel). The gun was designed for use against unarmored destroyers, so its high velocity was not needed to penetrate armor. Rather it made for a flatter projectile trajectory, which could compensate for fire-control errors. The resulting long gun was somewhat unwieldy, and because it used bagged powder, the 5-inch/51 could not be loaded readily when the weapon was at high elevation.
For antiaircraft fire, then, the Navy developed the lower-velocity 5-inch/25. Shrapnel from the gun’s large shell could damage an airplane at a distance, and its shorter barrel could be maneuvered rapidly to deal with fast aircraft. Limited muzzle velocity was acceptable because airplanes could not attack at very high altitudes. The ammunition was fixed (shell and powder packaged together), which made rapidly loading the gun easier, especially when it was elevated skyward.
Interwar arms-control treaties, meanwhile, put limits on the size of future battleships. Both the U.S. and Royal navies concluded that to save weight, those ships should have dual-purpose secondary guns instead of the earlier combination of special-purpose antiaircraft and antidestroyer guns. The U.S. Navy decided on a dual-purpose gun with a 5-inch bore, because existing U.S. battleships already used the two sizes of 5-inch guns.
The gun was conceived in the late 1920s, when the battleship-building “holiday” enshrined in the Washington Naval Treaty was expected to expire in 1931. In fact the subsequent London Naval Treaty extended the holiday to 1936. However, early in the 1930s the U.S. Navy began building destroyers for the first time since the end of the World War I “flush-decker” series. What armament should they have?
That depended on what the destroyers—and the Fleet—were likely to do. In the early 1930s, the U.S. Navy saw only one likely war on the horizon—against Japan (the Imperial Japanese Navy had a similar view regarding the United States). By this time the U.S. Navy was quite air-minded. American war planners envisaged a climactic fleet engagement somewhere in the western Pacific, after which a victorious U.S. Navy would blockade Japan. En route to the battle, the U.S. Pacific Fleet would pass through chains of islands mandated to Japan in the aftermath of World War I, including the Palaus and Marianas. Surely the fleet would have to fend off air attacks mounted from those places.
For the U.S. Navy, the evolving war plan made all the difference. The destroyers needed a heavy antiaircraft gun, ideally a heavy dual-purpose gun. And that was much the same weapon then being sketched out for future battleships—a compromise between the high-velocity 5-inch/51 and the handy but lower-velocity 5-inch/25.
For the gun to deal with surface targets—especially enemy destroyers attacking with torpedoes—the Navy wanted it to fire the heaviest possible shell. But a high rate of fire was also desirable; sailors would need to be able to easily pick up a round and shove it into the breach. The compromise was to use semifixed ammunition, so that the shell and its propellant cartridge were loaded separately. As it turned out, this did not unduly reduce the rate of fire.
After toying with a 5.4-inch/40 and then a 5-inch/40, the Bureau of Ordnance determined that a gun 38 calibers long—the 5-inch/38—fit the bill for battleships (and cruisers) as well as destroyers. It did not hurt that the Navy would combine the new gun with the best medium-caliber antiaircraft fire-control system of World War II, the Mark 37.
The prototype 5-inch/38 was delivered in 1933. As an indication of the sheer size of the weapon’s program, on 1 October 1941, before the wartime explosion of orders, 601 5-inch/38s were on hand afloat (962 had been completed) and another 3,318 were on order. Nearly all these guns were in dual-purpose mountings, the exceptions being twin single-purpose mounts (to save treaty-limited weight) on board 13 1,850-ton destroyer leaders. An estimated 2,168 base-ring mounts (such as those on destroyers), 3,298 simplified base-ring mounts, 1,347 twin mounts, and 161 pedestal mounts were produced, but it is not clear whether these figures include prewar production.
U.S. naval requirements were so great there were never enough 5-inch/38s to release the gun in quantity to allies; the largest delivery seems to have been 150 power mounts to the Soviet Union, probably for shore batteries. Before the Pearl Harbor attack, the British considered arming their own destroyers with 5-inch/38s, and the U.S. Navy rebuilt the British cruiser Delhi with the guns and a Mark 37 fire-control system.
Then the United States entered the war, and, despite British delight with the guns they had received, no more could be provided. Three Brazilian destroyers, conceived as license-built versions of the U.S. Mahans, were armed with 5-inch/38s installed in the United States, and the guns were planned for further Brazilian destroyers, but they were not installed until after the war. Plans to arm merchant ships with a version of the gun collapsed when the model was diverted to higher-priority programs such as naval auxiliaries and destroyer escorts.
Back in 1939, the Bureau of Ordnance had feared that the 5-inch/38 was obsolescent; airplanes were flying higher and faster, so shells had to reach higher and get there more quickly. The bureau designed a higher-velocity 5-inch/54; the twin 5-inch/54 was to have replaced the 5-inch/38 on board the last class of U.S. battleships (the Montanas), and it was to have armed the last class of cruisers designed during the war (the abortive CL-154s). The gun entered service in single rather than twin form, on board Midway-class carriers beginning in 1945. It then formed the basis for postwar power-loaded mountings, which were standard on board destroyers, frigates, and carriers starting in the 1950s. In common with other power-loaded (for rapid fire) postwar medium-caliber guns, they were less than successful. The Navy probably would have preferred to keep the reliable 5-inch/38.
As late as the 1970s, 5-inch/38s continued to serve in large numbers on destroyers whose lives had been extended under the Fleet Rehabilitation and Modernization program. The gun’s last active U.S. mountings were probably those on board Iowa-class battleships retired in the early 1990s. Many were exported on board ships transferred abroad beginning in the 1950s. The 5-inch/38 survives in active service on board two Gearing-class destroyers: the Mexican navy’s Netzahualcóyotl, formerly the USS Steinaker (DD-863), and the Pakistan Maritime Security Agency’s Nazim, formerly the USS Henderson (DD-785).
5-inch/38-caliber Mark 12/1 dual-purpose gun
Bore: 5 inches
Barrel length: 190 inches
Weight of projectile: 55 pounds
Propellant charge: 15.2 pounds
Muzzle velocity: 2,600 feet/second
Maximum range: 15,892 yards/27 degrees
17,414 yards/35 degrees
18,200 yards/45 degrees