Gato-class submarine

The "Gato" class of submarines was built for the United States Navy and launched in 1941–1943; they were the first mass-production U.S. submarine class of World War II. Together with their near-sisters the and es, their design formed the majority of the United States Navy's World War II submarine fleet. Named after the lead ship of the class, , the "Gato"s and their successors 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, boats of the "Gato" class were given the names of marine creatures. In some references, the "Gato"s are combined with their successors, especially the "Balao" class.
Design.
"AA-1" class and V-boats.
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, based on standard-type battleships since World War I. 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 battleships and cruisers. This was an operational concept born from experience in World War I. To operate effectively in this role, a submarine had to have high surface speed, long range and endurance, and heavy armament. Limitations in submarine design and construction in the 1920s and 1930s made this combination of qualities very difficult to achieve. The U.S. Navy experimented constantly with this concept in the post-World War I years, producing a series of submarines with less than stellar qualities and reliability, the (also known as the T class) and the V-boats, of which "V-1" through "V-3" were an unsuccessful attempt to produce a fleet submarine.
"Tambor" and "Gar" class.
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"-, -, and boats resulted in the "Tambor" and "Gar" classes. Finally, the U.S. Navy 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, as well as 20 years of submarine strategic concept development. It left the fleet submarine without a mission. 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.
"Gato" class.
The "Gato"-class design was a near-duplicate of the preceding "Tambor"- and "Gar"-class boats. The only significant differences were an increase in diving depth from to , and an extra five feet in length to allow the addition of a watertight bulkhead dividing the one large engine room in two, with two diesel generators in each room. The "Gato"s, along with nearly all of the U.S. Navy 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, hence the "partial" double hull. Operational experience with earlier boats 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 boats would be fully capable of routinely operating at 300 feet, a increase in test depth over the preceding classes.
The "Gato"s were slow divers when compared to some German and British designs, but that was mostly because the "Gato"s were significantly larger boats. 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 boat, which would 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 was flooded to provide a large amount of negative buoyancy at the start of the dive. Based on later wartime experience, the tank was normally kept full or nearly full at the surface, then 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 about 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 midwar, 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. No practical fix for this was available due to the limitations of the installed hydraulic systems used to move the rudder. Although a point of concern, the turning radius was still acceptable. After the war, a few fleet boats were fitted with an additional rudder topside at the very stern.
The class of boats had numerous crew comforts including air conditioning, refrigerated storage for food, generous freshwater distilling units, clothes washers, and bunks for nearly every crew member; these were 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. The air conditioning in particular had a very practical application, too, besides comfort. 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 . 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.
Engine changes.
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 General Motors Cleveland
16-278A V-type diesels. The other "Gato"-class boats received either the Fairbanks-Morse 38D 8-1/8 nine-cylinder opposed-piston engine or the 
General Motors Cleveland 16-248 V-type as original installations. These engines were hardy, rugged, and well liked by the crews and served the boats quite well.
Fairwater changes.
At the beginning of the war, "Gato"-class boats, 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. Most of the subs in postwar movies show the final result of these modifications. A side benefit of these modifications was the creation of convenient locations for antiaircraft guns.
Ships in class.
Seventy-seven of these boats were commissioned from November 1941 () through April 1944 (). Twenty of the 52 U.S. submarines lost in World War II were of this class, plus , a damaged boat that returned to the U.S., but was considered a constructive total loss and not repaired.
Occasionally, some confusion arises as to the number of "Gato"-class submarines built, with some sources listing the total as 73, due to the transitional nature of the first four boats (SS-361 through 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 hull numbers that fall in the middle of the range of numbers for the "Balao" class (SS-285 to SS-416, SS-425, and S-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 "Gato"s 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 through SS-364) to Electric Boat's "Gato"-class plans. Manitowoc's first "Balao"-class boat was .
World War II.
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. The first boat laid down was actually 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. "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 10 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 "Gato"s were built at four different locations (Electric Boat, Manitowoc, Portsmouth, and Mare Island).
All of the "Gato"s (with one exception, ) would eventually fight in the Pacific Theater of Operations. However, in the summer of 1942, six new "Gato"s 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 "Gato"s were in the thick of the fight against the Japanese. Many of these boats racked up impressive war records: , , and were the top three boats based on tonnage sunk by U.S. submarines. , "Flasher", and were third, fourth, and seventh place on the list for the number of ships sunk. "Gato"-class boats sank four Japanese submarines: , , , and ; while only losing one in exchange, to .
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 its designer, the Naval Torpedo Station Newport under the 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 torpedo weapons and was rushed into service in the fall of 1943. Unfortunately, it also 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 effective weapons, allowing the "Gato"s and other submarines to sink an enormous amount of Japanese shipping by the end of the war.
The "Gato"s 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 antiaircraft 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:
Variations on the above mods included the 1A (shortened navigation bridge), 2A (plating removed from periscope shears), and the 3A and 4A (which moved the SJ radar mast aft of the periscopes). The conning tower fairwater of "Flasher" is preserved in Groton, Connecticut, in the mod 4A 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 3-inch (76 mm)/50 caliber Mk. 17 gun (although some boats received older Mk. 6 mounts due to shortages). The 3-inch gun was the model originally specified for the "Gato" class, but war experience led to the removal of 4-inch (102 mm)/50 caliber Mk. 9 guns from old S-class submarines to equip front-line boats. Beginning in late 1943, almost all were refitted with a 5-inch (127 mm)/25 caliber Mk. 17 gun, and some boats had two of these weapons. Additional antiaircraft guns included single 40 mm Bofors and twin 20 mm Oerlikon mounts, usually one of each.
Postwar service.
At the end of World War II, the U.S. Navy found itself in an awkward position. The 56 remaining "Gato"-class submarines, designed to fight an enemy that no longer existed, were largely obsolete, despite the fact they were only two to four years old. Such was the pace of technological development during the war that a submarine with only a 300-foot test depth was going to be of little use, despite being modern in most other aspects. Enough of the "Balao" and "Tench" boats, with their greater diving depth, remained that the "Gato"s were superfluous for front-line missions. The Greater Underwater Propulsion Power Program (GUPPY) modernization program of the late 1940s largely passed these boats by. Only and received GUPPY conversions; these were austere GUPPY IB modernizations prior to their transfer to the Italian Navy. However, the U.S. Navy found itself new missions to perform, and for some of these the "Gato"s were well suited. The last two "Gato"-class boats active in the U.S. Navy were and , which were both decommissioned on 13 September 1969 and sold for scrap.
Radar picket.
The advent of the "kamikaze" demonstrated the need for a long-range radar umbrella around the fleet. 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. A submarine, though, could dive and escape aerial attack. After experimenting with the concept on several "Balao" and "Tench"-class boats, and realizing that a deep diving depth was not overly important in this role, six "Gato"s were taken in hand (, , , , , and ) for conversion. They were lengthened by to provide additional space for an air control center and had powerful air-search and height-finding radars installed, with the after torpedo room converted into an electronics space with torpedoes and tubes removed. They also received a streamlined "sail" in place of the traditional conning tower fairwater. Redesignated SSR and called the "Migraine III" conversion, these boats were only moderately successful in this role, as the radars themselves proved troublesome and somewhat unreliable. The radars were removed and the boats temporarily reverted to general-purpose submarines after 1959.
Hunter-killer.
The threat of the Soviet Navy building hundreds of Type XXI-derived submarines (eventually the 215-strong and dozens of others) in the Atlantic led the U.S. Navy to adapt submarines to specifically hunt other submarines, a radically new role for the 1950s. Concluding that this role did not require a fast or deep-diving submarine (this line of thought would quickly change with the advent of nuclear power), seven "Gato"s were converted to SSKs (hunter-killer submarines) between 1951 and 1953, joining three purpose-built "K-1"-class SSKs entering service at that time. The "Gato" class was chosen because large numbers were available in the reserve fleet should rapid mobilization become necessary, and the deeper-diving classes were more suitable for GUPPY rather than SSK conversions. A streamlined GUPPY-style sail was installed, a large sonar array was wrapped around the bow (losing two torpedo tubes in the process), the boats were extensively silenced including the removal of the two forward diesel engines, and they received a snorkel. was the test boat for the concept, having her sonar array at the forward end of the sail instead of the better position at the bow. The other boats in the program included , , , , , and . Eventually, more advanced sonars were installed on the new nuclear boats, with introducing the bow-mounted sonar sphere, and the SSK mission was folded into the regular attack submarine role. , commissioned in 1960, was an attempt to develop a slow but ultra-quiet nuclear-powered SSK equivalent, but no others were built. 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.
Guided missile submarine.
The Regulus nuclear cruise missile program of the 1950s provided the U.S. Navy with its first strategic missile capability. was converted in 1953 to house and fire this large surface-launched missile and was designated SSG (guided missile submarine). She could carry two of the missiles in a cylindrical hangar on the aft deck. She made strategic deterrent patrols with Regulus until 1964, when the program was discontinued in favor of Polaris.
Transport submarine.
With the retirement of the Regulus missile system in 1965, was converted into a troop transport in 1966. She was redesignated as an APSS (transport submarine), replacing in this role. Her Regulus hangar became a lockout chamber for UDT, SEAL, and Marine Force Recon teams in the Vietnam War. On 1 January 1969, "Tunny"s designation was changed to LPSS (amphibious transport submarine); however, she was replaced by and decommissioned in June of that year.
Submarine oiler.
 was converted to a SSO in 1950 to carry fuel oil, gasoline, and cargo to amphibious beachheads. She received additional "saddle" tanks wrapped around her outer hull to carry these fuels and a streamlined sail. After a few tests, the concept was dropped in 1951 as impractical, and "Guavina" served in the test role for a few years. In 1957, she converted back to the oiler/tanker role and carried the designation AOSS. This time, she experimented with refueling seaplanes at sea, which was potentially important, as refueling the nuclear-capable Martin P6M Seamaster at sea could improve the Navy's strategic strike capabilities. However, this mission, too, was dropped after a few years and "Guavina" was decommissioned.
Sonar test submarine.
The development of advanced sonar systems took on a great deal of importance in the 1950s, and several fleet boats were outfitted with various strange-looking sonar transducer arrays and performed extensive tests. Two "Gato"s, and (previously the prototype hunter-killer boat) were assigned to these duties and proved to be key players in the development of new sonar capabilities. "Grouper" had all her forward torpedo tubes removed and the space was used as berthing for technicians and as a sonar lab. "Flying Fish" was decommissioned in 1954, but "Grouper" continued in the test role until 1968.
Naval Reserve trainer.
Interested in maintaining a ready pool of trained reservists, the Navy assigned numerous fleet boats to various coastal and inland ports (even in Great Lakes ports such as Chicago, Cleveland, and Detroit) where they served as a training platform during the reservists' weekend drills. Twenty-eight "Gato"-class boats served in this capacity, some as late as 1971. In this role, the boats were rendered incapable of diving and had their propellers removed. They were used strictly as pierside trainers. These were in commission, but classed as "in commission in reserve", thus some were decommissioned and recommissioned on the same day to reflect the change in status.
Foreign service.
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. While most of these boats were of the more capable "Balao" and "Tench" classes, some "Gato"s went overseas, as well. Italy received two ( and ), which received the only GUPPY conversions given to "Gato"-class boats (Guppy IB). Japan received one (), Brazil two ( and ), Greece two ( and ), and Turkey two ( and ). The boats transferred to Japan and Brazil did not receive any modernizations (streamlining and snorkels) prior to transfer, but the four boats sent to Greece and Turkey did receive snorkels and partial streamlining to the fairwater.
Museum boats.
Six "Gato"-class submarines are open to public viewing. They primarily depend on revenue generated by visitors to keep them operational and up to U.S. Navy standards; each boat gets a yearly inspection and a "report card". Some boats, such as "Cod" and "Silversides", have been used in film production.
Surviving ships.
The following is a complete list of "Gato"-class museum boats: