The United States Navy Gato-class submarine formed the majority of the United States Navy's World War II submarine fleet. Named after the first vessel of this design, USS Gato, the Gato-class and its successors, the Balao and Tench classes, formed the core of the submarine service that was largely responsible for the destruction of the Japanese merchant marine and a large portion of the Imperial Japanese Navy in World War II. Gato's name comes from a species of small catshark. Like most other U.S. Navy submarines of the period, the Gato-class were given the names of marine creatures.
The Gato-class boats were considered to be "Fleet Submarines". The original rationale behind their design was that they were intended to operate as adjuncts to the main battle fleet. They were to scout out ahead of the fleet and report on the enemy fleet's composition, speed, and course, then they were to attack and whittle down the enemy in preparation for the main fleet action, a titanic gun battle between cruisers and battleships. This was an operational concept borne out of experience from World War I. In order to operate effectively in this role, a submarine had to have high surface speed, long range and endurance, and a heavy armament. State-of-the-art submarine design and construction in the 1920s and 1930s made this combination of qualities very difficult to achieve. The USN constantly experimented with this concept in the post-World War I years, producing a series of submarines with less than stellar qualities and reliability, the AA-1 class and the so-called V-boats.
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-, & Sargo-class boats resulted in the Tambor- & Gar-classes. Finally, the USN had hit the right combination of factors and now had the long-desired fleet submarine.
Timing, however, conspired against the actual use of these boats in their assigned role. The attack on Pearl Harbor on 7 December 1941 destroyed the Pacific Fleet battle line and along with it the concept of the battleship-led gun battle. The successful Pearl Harbor attack overturned 20 years of submarine strategic concept development and left the fleet submarine without a mission. Fortunately, the very 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
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. The inner pressure-resisting hull was wrapped by an outer hydrodynamic hull. The voids 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 because 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 affect 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, the 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 above 100 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.
Twelve submarines of this class built by Electric Boat received what would be the final installations of the Hooven-Owens-Rentschler (HOR) double-acting diesel engine. The Navy had been tinkering with this engine off and on since 1937 because its unique design promised nearly twice the horsepower in a package the same size as other diesel engine types. Unfortunately, the HOR company ran into severe design and manufacturing problems and these engines proved to be operational and maintenance nightmares. 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 GM-Winton 16-278A V-type diesels. The other Gato-class boats received either the Fairbanks-Morse 38D8 1/8 nine cylinder opposed piston engine or the GM-Winton 16-248 V-type as original installations. These engines were hardy, rugged and well liked by the crews and served the boats
These boats were authorized in appropriations for Fiscal Year 1941, as part of President Franklin Roosevelt's proclamation of "limited emergency" in September 1939. The first boat laid down was actually the USS Drum at Portsmouth Naval Shipyard on 11 September 1940. She was commissioned on 1 November 1941 and was the only Gato-class boat in commission when the war started. The Gato herself was laid down on 5 October 1940 by the Electric Boat Company at Groton, Connecticut and commissioned 31 December 1941. Due to their large construction capacity, more than half (41) of the class was built at Electric Boat facilities; three new slipways were added to the north yard and four slipways were added to the south yard to accommodate their production. In addition, the government purchased an old foundry downstream from the main yard, constructed ten slipways and turned the yard over to Electric Boat. Called the Victory Yard, it became an integral part of Electric Boat operations. A total of 77 Gatos were built at four different locations (Electric Boat, Manitowoc, Portsmouth, and Mare Island).
There is occasionally some confusion as to the number of Gato-class submarines built with some sources listing the total as 73. This is due to the transitional nature of the first four boats (SS-361 to SS-364) constructed under the second contract by the Manitowoc Shipbuilding Company of Manitowoc, Wisconsin. These were originally intended to be Balao-class subs and were assigned numbers that fall in the middle of the range of numbers for the Balao-class (SS-285 to SS-416 & 425–426). Manitowoc was a designated follow-on yard to Electric Boat; they used construction blueprints and plans supplied by Electric Boat and used many of the same suppliers. The government-owned shipyards (Portsmouth Naval Shipyard and Mare Island Naval Shipyard) began to make the transition to the new Balao design in the summer of 1942. Electric Boat, due to the huge backlog of Gato-class construction, was not ready to make the transition to the new design until January 1943. 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. Faced with a work stoppage while they waited for Electric Boat to catch up, managers at Manitowoc got permission to complete four additional boats (SS-361 to SS-364) to Electric Boat's Gato-class plans. Manitowoc's first Balao-class boat was USS Hardhead.
All of the Gatos (with one exception, USS Dorado) would eventually fight in the Pacific Theater of Operations. However, in the summer of 1942, six brand 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. All in all they conducted 27 war patrols but could not claim any verified sinkings. Considered a waste of valuable resources, in mid 1943 all six boats were recalled and transferred to the Pacific.
Once they began to arrive in theater in large numbers in mid-to-late 1942, the Gatos were in the thick of the fight against the Japanese. Many of these boats racked up impressive war records: Flasher, Rasher, and Barb were the top three boats based on tonnage sunk by US submarines. Silversides, Flasher, and Wahoo were 3rd, 4th, and 7th place on the list for the number of ships sunk. Gato-class boats sank four Japanese submarines: I-29, I-168 and I-351 and I-42; while only losing one in exchange, USS Corvina to I-176.
Their principal weapon was the steam powered Mark 14 torpedo in the early war years, with the electric Mark 18 torpedo supplementing the Mark 14 in late 1943. Due to a stunted research and development phase in the Depression-era 1930s, and in great part due to the arrogance and stubbornness of the Navy's Bureau of Ordnance, the "wonder weapon" Mark 14 proved to be full of bugs and very unreliable. They tended to run too deep, explode prematurely, run erratically, or fail to detonate. Bowing to pressure from the submariners in the Pacific, the Bureau eventually acknowledged the problems in the Mark 14 and largely corrected them by late 1943. The Mark 18 electric torpedo was a hastily copied version of captured German G7e weapons and was rushed into service in the fall of 1943. Unfortunately it too was full of faults, the most dangerous being a tendency to run in a circular pattern and come back at the sub that fired it. Once perfected, both types of torpedoes proved to be reliable and deadly weapons, allowing the Gatos and other submarines to sink an enormous amount of Japanese shipping by the end of the war.
The Gatos were subjected to numerous exterior configuration changes during their careers, with most of these changes centered on the conning tower fairwater. The large bulky original configuration proved to be too easy to spot when the boat was surfaced; it needed to be smaller. Secondly, the desire to incorporate new masts for surface and air search radars drove changes to the fairwater and periscope shears. Third, additional gun armament was needed and cutting down the fairwater provided excellent mounting locations for machine guns and anti-aircraft cannon. The modifications (or Mods) to the Gato-class conning tower fairwaters were fairly uniform in nature and they can be grouped together based on what was done when:
- Mod 1 – This is the original configuration with the covered navigation bridge, the high bulwark around the aft "cigarette" deck, and with the periscope shears plated over. All the early boats were built with this Mod and it lasted until about mid 1942.
- Mod 2 – Same as Mod 1 but with the bulwark around the cigarette deck cut down to reduce the silhouette. This also gave the .50 caliber machine gun mounted there a greatly improved arc of fire. Began to appear in about April 1942.
- Mod 3 – Same as Mod 2 but with the covered navigation bridge on the forward part of the fairwater cut away and the plating around the periscope shears removed. In this configuration the Gatos now had two excellent positions for the mounting of single 40 mm Bofors or twin 20 mm Oerlikon anti-aircraft cannon, an improvement over the .50 caliber machine gun. This mod started to appear in late '42 and early '43.
- Mod 4 – Same as the Mod 3 but with the height of the bridge itself lowered in a last attempt to lessen the silhouette. The lowering of the bridge exposed three I-beams on either side of the periscope shears. These exposed beams gave rise to the nickname "covered wagon boats". Began to appear in early 1944. The conning tower of USS Flasher (SS-249) is preserved in Groton, Connecticut in this configuration, with two single 40 mm Bofors mounts.
Deck guns varied during the war. Many targets in the Pacific War were sampans or otherwise not worth a torpedo, so the deck gun was an important weapon. Most boats began the war with a 4 inch (102 mm)/50 caliber gun, some with a 3 inch (76 mm)/50 caliber gun. The 3 inch was the gun originally specified for the Gato class, but war experience led to the removal of 4 inch guns from old S-class submarines to equip front-line boats. During 1944, almost all were refitted with a 5 inch (127 mm)/25 caliber gun, and some boats had two of these weapons. Additional anti-aircraft guns included single 40 mm Bofors and twin 20 mm Oerlikon mounts, usually one of each.
A Japanese boarding party from the destroyer Naganami inspected the grounded and abandoned USS Darter (SS-227). Documents disclosed weaknesses, later used to improve Japan's anti-submarine warfare.