The 3”/50 Part 1

Almost as soon as the airplane was recognized as a weapon of war, ships began to adopt various weapons to defend against them. Previous naval guns had only limited elevation, and through the First World War, only the main battery of capital ships had any director control. The complexity of anti-aircraft fire control quickly saw director controlled dual-purpose batteries adopted on even the smallest combatants.

One early weapon in the US Navy was the 3” gun. It had a barrel length of 50 calibers (150”) and was known as the 3”/50 (to distinguish it from the far less effective 3”/23). 

Mounted on a manually traversed and elevated pedestal, the 3”/50 was capable of engaging surface or aerial targets. It was a relatively simple weapon. A pedestal, tube, and a manually operated sliding wedge breech block. One gunner traversed the gun manually( the trainer), and another elevated it manually (the pointer). Another gunner was responsible for opening and closing the breechblock, and another for loading the gun. The loader would also used a fusesetter to set the mechanical time fuse. In early variants, the fuse was set by hand.  Other gunners brought ammunition to the loader. When fire control was available, the trainer and pointer elevated and trained the gun according to needles on a dial.  If director control was not available, optical sights on the gun mount were used.

Here’s a land based variant of the early 3”/50 being demonstrated.


The mount was not stabilized. That is, there was no compensation for the movement of the ship in pitch and roll. On a large vessel such as a cruiser or battleship or fleet tanker, that might not be such a huge problem, but in a smaller ship, such as a destroyer escort, the lively motion of the ship in even a slight seaway meant that accuracy suffered greatly.

The gun also had a relatively low rate of fire. A slow rate of fire reduced the chances that the fire control solution would be correct at the instance of firing. Marginally effective against 250mph planes in use at the beginning of World War II, even large barrages of guns were unable to cope with 400 mile an hour kamikazes by the end of the war. Clearly, something better was needed. We’ll take a look at that in Part 2.

4 thoughts on “The 3”/50 Part 1”

  1. The 3″/50 was common on smaller ships, as well as Auxiliaries when I was in. The Dealey Class DEs were armed with them (originally with an enclosed dual mount forward driven by an Anodyne motor) and an open dual mount aft. I don’t know if the after mounts were driven or manual.

    Sylvania had several open mount 3″/50. Can’t remember how many, but at least 4. The Mars class AFS ships were built in the 60s. DEs up through 1039 had 3″/50s. I think 1039 was built in the early 60s. As I recall, the Knox class DEs had a single 5″/54 forward with ASROC. They had nothing aft as they had a helo deck and hanger aft to carry a LAMPS ASW helo.

  2. The RN was not impressed with the 3″/50’s surface capabilities. A CAPTAINS class frigate CO said that,” it wouldn’t dent cold butter”, He wanted the ships refitted with the 5″/38, as the BUCKLEYs were stressed for them.

  3. I’ve seen some figures for planes destroyed vice rounds fired and the 3″/50 did not do as badly as might be expected. That was probably due to the fact that it was large enough to use VT fuses. Before that there was a clear preference for the 40mm, but once VT fuses were introduced they were competitive again.

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