To operate effectively in this role, a submarine had to have high surface speed, long range and endurance, and heavy armament.

[10] By 1931, the experimental phase of fleet submarine development was over and the Navy began to make solid progress towards what would eventually be the Gato class.

By 1940, a much better developed industrial base and experience gained from the Porpoise-, Salmon-, and Sargo-class ships resulted in the Tambor and Gar classes.

Fortunately, the same capabilities that would have enabled these submarines to operate with the fleet made them superbly qualified for their new mission of commerce raiding against the Japanese Empire.

Operational experience with earlier ships led the naval architects and engineers at the Navy's Bureau of Construction and Repair to believe that they had been unduly conservative in their estimates of hull strength.

Without changing the construction or thickness of the pressure hull steel, they decided that the Gato-class ships would be fully capable of routinely operating at 300 feet, a 50-foot (15 m) increase in test depth over the preceding classes.

Sufficient fuel bunkerage to provide the range necessary for 75-day patrols from Hawaii to Japan and back could be obtained only with a larger ship, which would take longer to submerge than a smaller one.

In an attempt to speed this process, additional limber, or free-flooding, holes were drilled and cut into the superstructure to allow it to flood faster.

Should a submarine submerge for any length of time, the heat generated by the recently shut-down engines, electronic gear, and 70 warm bodies will quickly raise internal temperatures above 100 °F (38 °C).

High humidity generated by tropical waters will quickly condense and begin dripping into equipment, eventually causing electrical shorts and fires.

[22] Frequent breakdowns and utter unreliability had destroyed these engines' reputation with the Navy and they were all removed at the first opportunity and replaced by General Motors Cleveland Model 16-278A V-type diesels.

The other Gato-class ships received either the Fairbanks-Morse 38D 8-1/8 nine-cylinder opposed-piston engine or the General Motors Cleveland Model 16-248 V-type as original installations.

[25] At the beginning of the war, Gato-class ships, as well as the Gar and Tambor classes, had fully shrouded fairwaters visually similar to modern nuclear submarines.

Experience during the war led to the progressive reduction of this structure to reduce visibility and radar profile at the expense of underwater performance and foul-weather operating comfort.

Twenty of the 52 U.S. submarines lost in World War II were of this class, plus Halibut, a damaged ship that returned to the U.S., but was considered a constructive total loss and not repaired.

Manitowoc had already completed their allotted production run of Gatos and could not switch over to the Balao design until Electric Boat supplied them with the plans.

[29][30] The Gato boats were authorized in appropriations for Fiscal Year 1941, as part of President Franklin Roosevelt's proclamation of "limited emergency" in September 1939.

However, in the summer of 1942, six new Gatos were assigned to Submarine Squadron 50 and sent to Rosneath, Scotland, to patrol the Bay of Biscay and to assist in the Operation Torch landings in North Africa.

Many of these ships racked up impressive war records: Flasher, Rasher, and Barb were second, third, and fourth based on tonnage sunk by U.S. submarines.

Once perfected, both types of torpedoes proved to be reliable and effective weapons, allowing the Gatos and other submarines to sink an enormous amount of Japanese shipping by the end of the war.

[37] The conning tower fairwater of Flasher is preserved in Groton, Connecticut, in the mod 4A configuration, with two single 40 mm Bofors mounts.

Surface ships refitted with powerful radar suites were put into service, but they proved vulnerable in this role, as they could be attacked as well, leaving the fleet blind.

Two Gato-class ships (Grouper and Finback) received rudimentary conversions to radar pickets before the end of World War II, but were not used in this role.

A streamlined GUPPY-style sail was installed, a large sonar array was wrapped around the bow (losing two torpedo tubes in the process), the ships were extensively silenced including the removal of the two forward diesel engines, and they received a snorkel.

Grouper was converted under project SCB 58 as the test ship for the concept, having her sonar array at the forward end of the sail instead of the better position at the bow.

[48] The slow and less capable diesel SSKs were decommissioned or reassigned to other roles in 1959, and all except Croaker and Cavalla (eventually preserved as memorials) were scrapped in 1968 and 1969.

On 1 January 1969, Tunny's designation was changed to LPSS (amphibious transport submarine); however, she was replaced by Grayback and decommissioned in June of that year.

Two Gatos, Flying Fish and Grouper (previously the prototype hunter-killer ship) were assigned to these duties and proved to be key players in the development of new sonar capabilities.

[53][54][55] The large numbers of relatively modern, but surplus U.S. fleet submarines proved to be popular in sales, loans, or leases to allied foreign navies.

They primarily depend on revenue generated by visitors to keep them operational and up to U.S. Navy standards; each ship gets a yearly inspection and a "report card".