127mm L/38 Dual-Purpose Artillery      Along with the Bofors 40mm L/56 and the Oerlikon 20mm guns, the 127mm L/38 -- the famous 5"/38 -- was probably the most effective U.S. armament employed during World War II, and very argueably the best all-round shipboard weapon of its type in any nation's naval service. 
      The design traced its origin back to the year 1928, when the United States began formally designing battleships for construction after the expiration of the Washington treaty. The increased aircraft and torpedo-craft threat made it desirable to employ a dual-purpose artillery, not only to save weight, but also to reduce costs. What was available immediately that could  
fulfil the role was the older 127mm L/25, a good AA weapon, but with too little muzzle velocity to be of much use against destroyers. The L/51, meanwhile, standard anti-torpedo gun of the old battleships, was not useable in the anti-air role. 
       A new design had to cope with the air threat, thus a shorter gun tube was desirable for good maneuverability; and with the odd surface target, high muzzle velocity was necessary. The General Board considered several calibers and caliber lengths, and finally came up with a modest refinement of the existing 127mm L/25 gun, which the L/38 resembled in general appearance. 
      The new gun was quickly procured for destroyers, fitting out the Farragut-class DDs as their first actual employment. The old battleships got none of them, for lack of funds. In addition, an entirely new series of directors was fitted to the destroyers. 
       Interestingly, though the gun was explicitly designed for dual-purpose work, the U.S. Navy employed it twice in mounts that could not elevate high enough to engage air targets, in order to buy more guns per ship. 
      Later classes, instead of trading such valuable anti-air firepower, favored the fewer-guns approach instead of being given a single-purpose artillery.  
      Enclosed mounts were being build for the Craven-subclass, and were mounted on all 
later destroyers until the Sumners. Similiarly, the heavy cruiser Wichita got four of these mounts (four more open mounts). 
       In order to protect cruiser and battleship secondaries from machinegun fire and shrapnel, the General Board next contemplated twin enclosed mounts for the L/25. This older gun was not deemed worth the extra money, and instead, the L/38 got the chance. This twin mount was fitted first to light cruisers Helena and St.Louis -- but would eventually see service on Essex carriers, Saratoga, the excellent Atlanta-class light cruisers, the new fast battleships, modern heavy and light cruisers, and finally, on a huge number of Sumner and Gearing class destroyers.  
      In the first year of the war, the L/38 played a big role in surface engagements, but a limited one, success-wise, in anti-air; it was attributed only some 5% of all kills made by U.S. anti-air equipment. However, by 1943, the ultra-secret VT proximity fuse made its arrival in shells, turning it into a deadly aircraft killer. How deadly was enhanced by the loading rate of the fabled 5-inch/38, which with experienced gunners became quite phenomenal for hand-loaded artillery. Surviving Japanese airmen interviewed postwar flatly declared that the Americans had been shooting a huge-caliber machinegun at them.  It remained in service aboard the Iowa class well into 1998. 
 

Stats

Year of Construction: 1934   Bore:  127mm/5in   Weight of gun: 3251 kg / 3200lbs    Weight of barrel: 1.812 tons / 1.783 tons   Length of gun: 5683mm / 223.8 ins.    Length of bore: ????mm / ???? ins.   Wt. of projectile: 25 kg / 55 lbs   Max. Range: 16.640m / 18.200 yds at 45° elevation   Ceiling: 11.340 m / 37.200 ft. at 85° elevation   Max. Elevation: 85°   Rate of Fire: 20 - 15 rounds/min

With well-received assistance by Frank Pierce Young.