Situation in 1940
In 1939, designs for a new class of submarine, closely resembling the Tambor Class were submitted and approved in response to President Roosevelt’s statement of “limited emergency”.
By 1940, the designing phase for the new class of submarine was complete, and the first boat of the new Gato Class, the USS Drum, was laid down for construction in September of that year. Drum was completed by November of 1941, just in time for the start of hostilities toward Japan.
Launching of USS Robalo at Maniwotoc Shipbuilding Co, 9 may 1943.
The Gato Class of diesel-electric submarines had a length of 311 feet (95 meters), a draft of 16-17 feet (4.8-5.1 meters), and a beam of 27 feet (8.3 meters), with a displacement of 1,525 tons while surfaced and 2,424 tons while submerged.
A conning tower was placed near the front-middle part of the deck where the periscopes and anti-aircraft guns were located. A deck gun was mounted either on the bow or stern of the deck.
The boat was relatively cramped, as 60 crew members had to stay in a space only slightly longer than an American football field for up to months at a time. The smells were often horrible, crew could only shower a couple of times a week, and casualties were high.
USS Bar (SS-220)
American submarines and the Gato Class in particular were some of the most heavily armed of the war, with armament comparable to some surface ships.
Standard armament of a Gato Class boat was 1x 40mm Bofors Anti-aircraft cannon, 1x 20mm Oerlikon Anti-aircraft cannon, and 1x 3 inch (76mm) or 5 inch (127mm) deck cannon. On some Gato Class subs, the 3 inch gun was replaced with a larger 4 inch one. Additionally, small arms such as the M3 Grease Gun or M1 Thompson were carried for boarding and security, and M2 Browning machine guns were also carried.
As for underwater armament, the Gato had 10x 433mm torpedo tubes, 6 fore and 4 aft. These fired the Mark 10 and often problematic Mark 14 torpedoes, which were later supplemented by the Mark 18 electric torpedo.
USS Trigger, Mare island Navy Yard, April 6 1942
USS Wahoo, SS-238
4 electric motors driven by 4 diesel engines powering 2 propellers gave the Gato Class a top speed of 21 knots while surfaced and 9 knots while submerged.
As opposed to German submarines at the time which used diesel transmission on the surface and electric transmission subsurface, American diesel-electric engines used on the Gato and Balao Class submarines used diesel engines to charge electric batteries and power an electric motor. This had multiple advantages, as it allowed for the diesel engines to run at a high speed without breakdown. It also allowed the diesel and electric motors to run at different speeds, giving to freedom for one or more of the diesel engines to be shut off for maintenance while the others kept working.
While at 10 knots, the Gato had a range of 20,000 km (11,000 nm, 12,400 mi), enough to get it from Hawaii to Japan and back.
While submerged, a typical Gato Class boat could stay underwater for up to 48 hours at a speed of 2 knots, however this rarely had to happen as most attacks would be done in half that time.
USS Gato, 30 december 1941
The Gato Class served from 1941 to 1969 in 6 different navies. It served in both the Atlantic and the Pacific during World War 2, with the most successful boat sinking more than 60,000 tons of merchant shipping. It can be safely assumed that Gato Class submarines sank in excess of 200,000 tons of shipping, although numbers vary across sources.
The role of the Fleet boats, which included the Porpoise, Salmon, Tambor, and Sargo Classes and later the Gato Class was to protect the US Fleet while on patrol. However, after Pearl Harbor fleet tactics drastically changed, and so the Fleet submarines would have to change as well. Fortunately for the US Navy, the Fleet type submarines were perfect for attacks on Japanese merchant shipping as they were fast, could carry lots of fuel, and were heavily armed.
As soon as hostilities opened between the Axis Powers and the United States, Gato Class submarines were sent on patrol. Most submarines were based out of Hawaii, Australia, and while it was still under US control, the Philippines. Attacks and patrols were conducted from the Java Sea to the Sea of Japan and everywhere in between.
USS Drum, SS-228 in Mobile, Alabama
There were also a limited amount of Gato submarines that were based out of Scotland for a short time, before they were considered a waste of resources as German shipping in the area was rather limited and thus the subs were sent back to the Pacific theater of operations.
After World War 2, the US Navy still had plenty of surplus Gato Class submarines. While many were sold to allies that were rebuilding their navies, some were kept to carry out other duties that other submarines couldn’t do. These included hunter-killer patrols, radar picket duties, and guided missile carrying.
USS Grouper as AGSS-214, underway circa 1961
Radar Picket Boats
With Kamikaze attacks and air raids becoming more frequent, 6 Gatos were increased in length by 24 feet and had their aft torpedoes removed to make room for more radar equipment. This allowed for early warning against aircraft for American fleets.
Hunter Killer Boats
After World War 2, the Soviet Union began to mass-produce late war German Type-XXI U-Boats under the designation of Whiskey Class. These could be very dangerous to American and European ships in the Atlantic, so 7 Gato boats were converted to dedicated Hunter-Killer subs by adding sonar equipment and removing a pair of diesel engines to reduce sound. A snorkel was also added to allow the subs to stay underwater for a much longer period of time.
Gato Hunter-Killer submarines remained in service until 1959, until they were scrapped or turned into memorials.
Guided Missile Carrier and UDT/SEAL Transport
In 1953, a single Gato submarine (USS Tunny) was converted to be able to fire Regulus nuclear missiles. She served in this role until 1964, when she was converted once again to be able to transport UDT/SEAL teams to and from missions.
USS Tuny, SSG-282 Regulus launching sequence
USS Flounder, SS-251, July 1945
The Gato Class would see 77 models produced at $2.6 million until 1944, when it was replaced by the Balao and Tench classes in production. The Gato would see service in 6 different navies until 1969, when it was ultimately replaced by more modern diesel-electric and nuclear powered submarines.
Even though it wasn’t necessarily the best submarine of World War 2, the Gato Class undoubtedly had an impact on the Pacific Theater and on submarine design in general. Ships, weapons, and tactics were developed just to counter American submarines, with the Gato making up the majority of the US submarine fleet during the early parts of the war.
USS Cod postwar
Specifications (Gato class)
-Displacement: 1,525 tons surfaced, 2,424 ton submerged
-Dimensions: 312 x 27 x 17 feet
-Propulsion: 4 Fairbanks-Morse Diesel Engines, 4 Electric Motors, 2 Sargo Batteries, top speed of 21 knots surfaced or 9 knots submerge
-Armament: 1 Bofors 40mm cannon, 1-2 Oerlikon 20mm cannons, 1 3 inch/5 inch deck cannon, 10 533mm torpedo tubes
-Crew: 6 officers, 54-64 enlisted sailors
USS Gato (1/700)
USS Tench (1/700)
USS Grunion, SS-216
USS Harder, 1945, Mare Island Navy Yard
USS Tench, HD 1/400 illustration