Few naval weapons were more ubiquitous in World War II than the 5”/38 gun. In four main configurations, and dozens of minor ones, the 5”/38 served as the secondary battery of battleships, and cruisers, the main battery of carriers, some cruisers, destroyers, destroyer escorts, as well as arming countless fleet auxiliaries and merchant ships.
Entering service in the mid-1930s, the 5”/38 was, in terms of barrel length, a compromise between the earlier 5”/51 single purpose gun used as the secondary anti-ship battery on older battleships, and the 5”/25 anti-aircraft gun used on some battleships and cruisers. The 5”/51 was too large to be made as a dual purpose gun, and its modified Wellin breech screw wasn’t suited to rapid fire. The 5”/25, with a manually operated sliding wedge breech block, had a good rate of fire, but had a limited maximum vertical range due to its short barrel. The compromise 5”/38, capitalizing on advances in technology, used an automatic vertical sliding wedge breechblock, and added a hydraulic rammer to seat home the projectile and powder case.
When we talk about the gun, in whatever configuration, we are generally talking about the gun itself and the mount. The gun was pretty much always the Mk12 gun assembly, which was the gun barrel, the breech assembly, the recoil system and hydraulic rammer. The difference was in the four main types of mounts.
The simplest mount was a basic, open pedestal mount. It could be bolted onto just about any flat surface on a ship. Electrical power and high pressure air had to be provided, but that’s easy enough on just about any ship. It was the first to enter service, on a small batch of pre-war destroyers. This same mount would also arm many auxiliaries such as transports and tankers. Projectiles and powder cases for the gun were stored in ready service boxes located near the mount. These were passed by hand to the mount, where the projectile man and the powder man laid them on the loading tray, and activated the rammer.
The other three main types of mounts were all “base ring” mounts and all used an “upper handling room” and lift hoists. There were single base ring enclosed mounts, twin base ring enclosed mounts, and open single base ring mounts.
Twin 5”/38 mount, upper handling room, magazine, and powder room.
The “base ring” mounts meant the gun wasn’t mounted on a pedestal, but rather a roller ring with an open space through which shell and powder hoists pass through. The hoists are affixed to the gunhouse, and rotate with it. The lower hoists are fixed in place. The advantage of the base ring mounts were in a greater rate of fire, and ability to sustain fire for longer periods than the pedestal mounts, which you’ll recall are served by ready ammunition boxes.
The three “base ring” configurations were:
1. Open single mount- specifically for the mounting on the sponsons of Essex class aircraft carriers
2. Enclosed single mount- main battery on the Benson/Gleaves class, and Fletcher class destroyers, also on late production destroyer escorts and numerous auxiliaries.
3. Enclosed twin mount- main battery of anti-aircraft cruisers, Sumner/Gearing class destroyers, secondary battery for modern battleships and cruisers, and on the flight deck (starboard side) of Essex class carriers.
The 5”/38 was effective against both surface and airborne targets. In the early years of the Pacific War, surface combat between ships of the US and Japanese fleets was quite common, and the 5”/38 threw more than a few rounds at Japanese destroyers, cruisers and even battleships. And as fire support for amphibious warfare became more and more critical to the war, the 5”/38 fired more and more rounds. We tend to think of the massive numbers of 6”, 8”, 14” and 16” projectiles fired by cruisers and battleships, but the fact is, stupendous numbers of 5” rounds were fired either in prelanding bombardments, or as call fires for troops ashore. Indeed, across the Atlantic, without the timely and devastatingly accurate fire of 5” guns of the destroyers in support, the landings at Omaha Beach may well have failed. Destroyers braved mined waters, potential grounding, and German counterfire to close within spitting distance of the shore to bring their 5” guns to bear. It’s worth noting that the first message V Corps sent after establishing itself ashore was “Thank God for the US Navy.”
The gun was designed from the beginning as an anti-aircraft weapon, but the perceived threat of the 1930s was not at all what the real threat of the 1940s turned out to be.
The perceived threat of the 1930s was largely seen as fleets of high altitude level bombers laying down patterns of bombs on the fleet. Accordingly, the 5”/38 was expected to fire barrages of time fused shells in flak patterns. Both the gun and its associated Mk37 Fire Control System (and the remarkable Mk1 Ford mechanical computer) were optimized for this mission. The Mk37/Mk1 combination would determine the superelevation and firing bearing as well as determine the fuse setting. The hoists of the upper handling room actually served as fuse setters, updating the time fuse setting automatically until the round was removed from the hoist for loading.
But the air threat of the war was actually quite different. High altitude bombers had great difficulty hitting discrete stationary targets such as bridges. Hitting a twisting, turning ship moving at 30 knots was virtually impossible. It turned out low flying torpedo bombers and dive bombers were to be the threat to beat, until the appearance of the Kamikaze suicide attacker. When the VT proximity fuse appeared, the 5”/38 became the most effective anti-aircraft weapon of the fleet. Its good rate of fire, large effective bursting radius, good range, and effective fire control meant the 5”/38 had a better chance of stopping an attacker than any other weapon. The problem was, with only one or two directors available per ship, each ship was vulnerable to saturation attacks. While the guns and director were busy shooting down one plane, another was busy closing in for the kill. Reading the history of the fleet at Okinawa, there are story after story of destroyers knocking down five, six Kamikazes, only to be swamped by the seventh, eighth and ninth planes.
With the dawning of the jet age, increasing aircraft speeds meant the effectiveness of the 5”/38 as an anti-aircraft weapon steadily declined. It was still an excellent anti-surface weapon, effective out to about 9 miles. Further, the enormous fleet of war-built ships equipped with it meant that mounts in various configurations would continue to serve for several decades more (the last mounts in US service were aboard the Iowa class battleships, but surplus Navy ships mounting them can still be found in some 3rd world navies).
Faced with the need for improved anti-aircraft performance, the Navy began development of guns with higher performance. The Midway class carriers, built at the end of the war, were armed with an improved 5” inch gun with a 54 caliber barrel for higher velocity. These base ring single enclosed mounts were arrayed on the sponsons on both the port and starboard sides. No other classes employed this mount. Other than the longer barrel, it was virtually identical to the earlier 5”/38.
When the Navy finally began to build replacements for the WWII era destroyers, the 5”/38 was first replaced by the Mk42 5”/54. The Mk42 was a “fully automatic” weapon, with the entire loading process being mechanical. Theoretically, the new mount had a higher rate of fire, but the mechanical loading was temperamental, and prone to jamming.
Beginning with the Spruance class destroyers in 1975, the Mk42 was replaced by the Mk45 Lightweight 5”/54. The LW Mk45 was completely unmanned. By accepting a lower rate of fire, it gained mechanical reliability. The current production variant of the Mk45 has a still longer tube, at 62 calibers.
Most anti-aircraft functions of the 5” gun were taken over by a series of anti-aircraft missiles. Maybe we’ll address the Navy’s anti-air missiles in another series.