​Class Design

The Gato-class design was a near duplicate of the preceding Tambor & Gar-class boats. The only significant difference was five feet in length added to the engine room section to allow the addition of a watertight bulkhead, dividing the one large engine room in two, with two diesel generator sets in each room. The Gatos, along with nearly all of the USN fleet-type submarines of World War II were of partial double hull construction. An outer hydrodynamic hull wrapped the inner pressure-resisting hull. The void areas between the two hulls provided space for fuel and ballast tanks. The outer hull merged with the pressure hull at both ends in the area of the torpedo room bulkheads, thus the "partial" double hull. Operational experience with earlier boats led the naval architects and engineers at the Navy's Bureau of Construction & Repair to believe that they had been overly conservative in their estimates of hull strength. Without changing the construction or thickness of the pressure hull steel, they decided that the Gato-class boats would be fully capable of routinely operating at 300 feet, a 50 foot increase in test depth over the preceding classes.

The Gatos were slow divers when compared to some German and British designs, but that was mostly due to the fact that the Gatos were significantly larger boats. Sufficient fuel bunkerage to provide the range necessary for 75 day patrols from Hawaii to Japan and back could only be obtained with a large boat, which will take longer to submerge than a smaller one. Acknowledging this limitation, the Bureau designers incorporated a negative (sometimes called a "down express") tank into the design, which provided a large amount of negative buoyancy at the start of the dive. Normally kept full or nearly full at the surface, the tank was emptied to a certain mark after the boat was submerged to restore neutral buoyancy. At the start of the war these boats could go from fully surfaced to periscope depth in approximately 45–50 seconds. The superstructure that sat atop the pressure hull provided the main walking deck when the boat was surfaced and was free flooding and full of water when the boat was submerged. When the dive began the boat would "hang" for a few extra seconds while this superstructure filled with water. 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. By mid war, these measures combined with improved crew training got dive times down to 30–35 seconds, very fast for such a large boat and acceptable to the boat's crew,

The large size of these boats did negatively impact both surfaced and underwater maneuverability when compared to smaller submarines. There was no practical fix for this due to the limitations of the installed hydraulic systems that were used to move the rudder. Although a point of concern, turning radius was still good enough to be acceptable. After the war, a few fleet boats were fitted with an additional rudder topside at the very stern.

These boats all had air conditioning, refrigerated storage for food, fresh water distilling units, clothes washers, and bunks for nearly every crew member; luxuries virtually unheard of in other navies. The Bureau designers felt that if a crew of 60-80 men were to be expected to conduct 75 day patrols in the warm waters of the Pacific, these types of features were vital to the health and efficiency of the crew. They could be added without impact to the boat's war fighting abilities due to the extra room of the big fleet boat. However, one feature in particular had a very practical side to it. Submerge a submarine for any length of time and the heat generated by the recently shut down engines, electronic gear, and 70 warm bodies will quickly raise internal temperatures into the 100's Fahrenheit. High humidity generated by tropical waters will quickly condense and begin dripping into equipment, eventually causing electrical shorts and fires. Air conditioning, acting mostly as a dehumidifier, virtually eliminates this problem and greatly increases mechanical and electrical reliability. It proved to be a key factor in the success of these boats during World War II.

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