American submarines underwent a number of modifications during the Second World War. These included changes to the gun armament, detection gear, electronics suites, and even the exterior appearance of the boats themselves.

Salmon as built

Pre-war Gatos and other classes, like the U.S.S. Salmon (pictured), started out with large, well-sheltered (for a submarine) conning tower fairwaters, with an enclosed forebridge featuring glazed deadlights, and a surface steering position. From the viewpoint of the conning officer and helmsman, this had obvious advantages. They were out of the weather, and the helmsman could see where he was going when the boat was surfaced.

There was no radar. The deck gun was located aft of the conning tower fairwater. Anti-aircraft weaponry was limited to machineguns, which had to be brought up from below and mounted before they could be used. The 3″/50 deck gun, if that was fitted, could potentially have been used as an anti-aircraft weapon, as it possessed a dual purpose mount that would allow sufficient elevation, but submarines were not issued appropriate ammunition and lacked the fuse setters that would have been needed to use air-burst rounds. Some fleet boats had heavier 4″/50 or 5″/50 deck guns, taken from retired S-boats, which had low-angle mounts and would have been essentially useless in an anti-aircraft role even with the proper ammunition.

The sheltered bridges were just about the first thing to go once the war started. Initially, the deadlights were either plated over, or covered with paint, to eliminate a source of reflection that might give away the boat’s presence. Since the helmsman could no longer see through the deadlights, the upper steering position was removed.

Salmon after refitThe second picture shows Salmon after a 1943 refit. Note that the tall fairwater has been cut down fore and aft to create platforms for anti-aircraft weapons. These were usually standard 20mm single-barrel Oerlikons which, while not designed to be submerged, were found to tolerate it well enough as long as the barrels were changed frequently. The upper bridge was faired in to form a smaller area where the old upper bridge had been located, and a venturi shield fitted across the front. The idea was that it would keep spray out of the bridge, though it seemed to be no more effective than any other spray shield. On theGatos, the plating on the periscope shears was removed. The primary purpose was to reduce the silhouette, making it harder to see the boat on the surface.

The deck gun has been moved to the forward deck. Whether the gun itself has been changed is difficult to tell from the photo. Above the bridge, SJ radar has been added forward of the periscope shears. Later in the war, this was usually moved to a position abaft the shears. The extended mast for the SD radar is clearly visible at the rear of the bridge. While not really visible in this picture, pressure-proof ready use ammunition lockers would have been added at the front and rear of the fairwater for the deck gun, and under the bridge for the 20mm. Pressure-proof stowage was also added on the bridge for the machineguns, eliminating the need to bring them up from below.

Other wartime modifications weren’t always as obvious. Continuous improvements were made in the TDC, to include new inputs as radar was added, or to improve performance. PPI was added to the radar. Engines and motors were upgraded, and wiring replaced. In the case of the boats with H.O.R. engines, the engines were replaced entirely.

Kingston valves, which are used to close the bottom of the ballast tanks, were removed to increase diving speed (and to scavenge the tin they contained). As a consequence, the boats would “ride the vents,” staying afloat on the air trapped in the ballast tanks. The vents themselves were often enlarged. Additional limber holes were added to the superstructure, so that any trapped air could escape more rapidly, which also sped up diving. It was also common practice for the commanders to keep the negative tank full when running surfaced, greatly increasing diving speed.

The original 3″/50 deck guns were generally replaced with something heavier. In Salmon‘s case, it appears that a 4″/50 has been mounted. Once it became available in sufficient quantity, the 5″/25 wet mount was the preferred weapon. If these guns were available, the commanding officers had the option of shipping a pair. A rudimentary central fire-control director was also available late in the war. The 20mm guns could also be replaced with single-mount 40mm Bofors guns, if available.

The individual commanders had a great deal of leeway on gun armament, and could equip their boats pretty much as they wished, as long as the guns were available and appropriate. It might be noted that the anti-aircraft weapons, whether 20 or 40mm, were almost never used for shooting at enemy planes. Instead, it was mostly used for attacking sampans and other small enemy shipping, where a torpedo, or even the heavier shells from the deck gun, might be considered wasteful.

As for shooting at enemy planes, American commanders were trained to get the boat under water, where it was virtually immune to machinegun and cannon fire, rather than risk shooting it out on the surface.

Various camouflage paint schemes were tried during the war. These ranged from simply painting the entire boat black, to various geometric patterns intended to break up the outline and make the boat difficult to see on the surface. In the end, the standard pattern was to paint all horizontal surfaces flat black and all vertical surfaces haze gray. As a result, a surfaced fleet boat tended to fade into the horizon from the surface while, from the air, a submerged boat would either not be seen or possibly be mistaken for a whale.

Additional Reading:

U.S. Submarines Through 1945: An Illustrated Design History