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Introduction to the Gato-class submarines

The Gato-class fleet submarines, of which there would eventually be a total of 77 boats, were authorized in Congressional appropriations on June 14, 1940 for Fiscal Year (FY) 1941. This was the so-called Two Year Program. It called for additional 21,000 tons of submarines over and above what the Navy already had. The ink wasn't even dry on this authorization when the fall of France and the deteriorating situation in China prompted Congress to implement the add-on 70 Percent Expansion Act on July 19, 1940. This act authorized an additional 70,000 tons of submarine construction, for a total of 43 more boats, over and above the boats in the Two Year Program. Delighted with the new appropriations, the Navy's Bureau of Construction & Repair (C&R) chose to standardize on a single design for mass production. The new submarines, to be named the Gato-class, were slightly modified versions of the FY-39 and 40 submarines, the Tambor/Gar-class.

A "fleet submarine" was a large submarine intended to operate directly with the main fleet battle line composed of battleships, aircraft carriers, cruisers, and destroyers. Their role was to range out ahead of the battle line and act as scouts. They were to find the enemy and report on their composition, course, and speed. They were to then conduct attrition attacks designed to weaken the enemy fleet prior to the main gun battle with the U.S. battle line. To accomplish this mission the submarines had to have a long range, high speed, and be heavily armed. The subs also had to be quite large in order to fit all of the necessary equipment to achieve these qualities into the pressure hull.

Early development

The USN's earliest submarines were of the harbor defense, coastal defense, and patrol types and thus were too small, too underpowered, and lacked the necessary range to conduct the fleet submarine role. The Navy's first attempt to build a fleet submarine was the T-class of 1916 and 1917. The state of the art in those years lacked the technology needed to provide the powerful engines and refined hull form required to get the high speed and sea-keeping qualities that the boats needed. The T-class was an expensive failure, but the Navy learned was wasn't going to work and rolled those lessons into future construction, which would become the V-class submarines of the 1920s and early 30's.

The nine V-class submarines ended up being largely experimental in nature, as the Navy tinkered with several concepts brought out by WW I. The class not only consisted of fleet submarines, but also a specialized mine layer, two commerce raiding cruiser submarines, an open ocean patrol submarine, and two small fleet boats. The boats were either too big, too small, or they were too experimental in nature to be fully successful. All of them were underpowered, as diesel engine technology in the United States badly lacked in comparison with European designs.

The experience with the T and V-classes had taught the Navy what worked and what didn't when it came to building a fleet submarine, and by 1933 they had moved beyond the experimental stage and began solid progress towards what would become the Gato-class. The ten Porpoise-class boats of 1933-1937 and the 16 Salmon/Sargo-class boats of 1936-1939 were largely successful and proved to be solid steps up the developmental ladder. The 12 Tambor/Gar-class submarines of 1939-1941 were the ultimate peacetime refinement of the fleet submarine concept. Large, fast, and powerful these boats were highly regarded by the Submarine Service and their crews. When the FY-41 appropriation programs were being discussed, it was decided to "freeze" the design at that point for mass production. These boats became the famed Gato-class.

The Gato-class

The Gatos were, as expected, very similar to the preceding Tambor/Gars. The Gatos were lengthened by five feet in order to accommodate a watertight bulkhead that divided the Tambor/Gar's one large engine room into two smaller ones. The C&R designers also realized that they had been overly conservative with the rating for the previous boat's maximum submerged safe operating depth (test depth) and with a stroke of a pen rated the Gato class with a test depth of 300 feet (91.5 m), a 50 foot increase over the Tambor/Gars. There were other refinements as well, like making both of the periscope eyepieces usable in the conning tower (a separate watertight compartment above the central control room) instead of the control room, essentially "lengthening" one of the periscopes.

The boats were engined with four now fully refined Fairbanks-Morse or General Motors Winton diesel engines in a "diesel-electric" arrangement, where the engines drove only electrical generators, and the electricity produced was sent to electric motors on each propeller shaft, or to recharge the batteries used for submerged propulsion. The FM and GM engines were hardy, rugged, reliable, and well liked by the crews and provided excellent service. Unfortunately, eight submarines of the class were equipped with Hooven, Owens, & Rentschler (HOR) 99DA diesel engines, which for several reasons were complete failures. Those subs were eventually re-engined with GM Winton units during wartime overhauls.

In early 1942 the Gatos and other USN submarines began to be equipped with a remarkable device: radar. The first sets were designated SD and were used to detect incoming aircraft while the submarine was surfaced. This gave the crew an advanced warning of danger in the area and gave the commanding officer information vital to keeping his boat safe. The second type was designated SJ and was used to detect surface targets day or night and in any weather condtions. The SJ radar was accurate enough to precisely track targets even when they couldn't be seen visually. The tactical advantage that this gave USN submarines can not be overstated; indeed it was a prime factor in the eventual overreaching success of the submarine campaign against Japan.

The Gatos (like many of their predecessors were equipped with an advanced version of the Torpedo Data Computer (TDC), an analog computer that was used to accurately aim torpedoes. The Mark III TDC consisted of two components: the Position Keeper (PK) and the Angle Solver (AS). Using automatic inputs for the submarine’s own course and speed, the operators input the target’s length, estimated speed, and angle on the bow based on periscope observations or radar tracking. The PK then solved the equations for motion integrated over time, and provided a continuous estimate of the target’s position. The AS took that input from the PK, combined it with the tactical properties of the torpedo, and solved for the needed torpedo gyro angle. It then transmitted this information to the weapons in the tube, and set the gyrocompass of the weapons automatically so that they would turn to a course to intercept the target once they left the tube. This was a significant tactical advantage, and the TDC became the envy of the world's navies.

Significantly, like all submarines built since the Salmon/Sargo-class, the Gato-class boats were built to an all-welded construction method, as opposed to the more traditional riveted method. Welding made for strong and resilient pressure hulls that could take a lot of punishment and still survive.

The Gatos also had air-conditioning, a complete refrigeration plant for storage of food, stills for making plenty of fresh water, clothes washing machines, and enough bunks so that every crew member could have one of their own. Food was of uniformly very high quality, the best in the fleet, prepared in compact galleys that turned out the food in prodigious quantities. These were luxuries virtually unheard of in foreign navies, but they were absolute necessities if the crew were expected to conduct 60-90 patrols in the warm waters of the Pacific Ocean.

These qualities made the Gato-class a nearly ideal member of the nearly 232 submarines that the USN commissioned during the war. Along with the previous classes, and the follow-on Balao and Tench-classes, the Gatos had a significant and disproportionate effect on the outcome of the Pacific war, shooting the bottom out of the Japanese Merchant Marine and crippling operations of the Imperial Japanese Navy.

Class Construction

The sheer numbers of submarines that the Navy ordered nearly overwhelmed the existing production sources.

The Victory Yard

USS Dorado (SS-248)

Specifications

Sea Trials

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