Gato-class Submarine

1. Lead

The Gato-class submarine was the United States Navy’s first mass-produced fleet submarine and the boat that carried the American submarine war against Japan through its hardest year. Designed in the late 1930s to meet the Navy’s requirement for a long-range submarine that could operate with the battle fleet across the vast Pacific, the Gato combined a range of about 11,000 nautical miles, a surface speed of more than 20 knots, and an armament of ten torpedo tubes and 24 torpedoes.

Seventy-seven boats were completed between 1940 and 1944, and they formed the core of the submarine force that, by the end of the war, had sunk more than half of all Japanese ships lost. The class’s most famous boats — USS Wahoo, USS Growler, USS Harder and USS Flasher — became legends in the submarine service, and the Gato’s design, improved only in its pressure-hull steel, became the Balao-class submarine that followed it.

The Gato was not the first American fleet submarine, but it was the first that was right. Earlier classes had been too slow, too short-ranged, or too lightly armed for the Pacific war the Navy expected to fight. The Gato got the balance right, and it did so in time: the first boats were commissioning as the war in Europe began, and the class was in full production when Japan attacked Pearl Harbor.

Its crews fought with a faulty torpedo for the first two years of the war, against an enemy that learned quickly to protect its shipping, and in waters thousands of miles from base — and they won. This article describes the Gato’s background and development, its design, its variants, its operational history, its performance, its operators, its legacy and the examples that survive.

2. Key Facts

Type	Fleet submarine (diesel-electric)
Origin	United States
Designers	Bureau of Ships; Electric Boat Company
Builders	Electric Boat (Groton), Portsmouth Naval Shipyard, Mare Island, Manitowoc
In service	1941–1969 (US Navy); longer with foreign navies
Produced	1940–1944; 77 completed
Displacement	About 1,525 tons surfaced; about 2,424 tons submerged
Length	311 ft 9 in (95.0 m)
Beam	27 ft 3 in (8.3 m)
Draught	16 ft 10 in (5.1 m)
Test depth	300 ft (91 m)
Propulsion	4 diesel engines (5,400 hp surfaced); 4 electric motors (2,740 hp submerged); 2 shafts
Speed	About 20.25 knots surfaced; about 8.75 knots submerged
Range	About 11,000 nautical miles at 10 knots surfaced
Crew	6 officers, 54 enlisted men
Armament	10 × 21-in torpedo tubes (6 bow, 4 stern); 24 torpedoes; 1 × 3-in deck gun (later 5-in); 20 mm and .50-calibre anti-aircraft guns
Most famous boats	USS Wahoo (SS-238), USS Growler (SS-215), USS Harder (SS-257), USS Flasher (SS-249)

3. Background and Development

A submarine for the Pacific

The Gato was designed for a war the United States Navy had been planning for twenty years: a war with Japan, fought across the Pacific, in which the fleet would advance from Hawaii to the Philippines and then to the coast of Japan, and in which submarines would scout ahead of the fleet, attack Japanese warships, and cut the sea lanes between Japan and its empire.

That war demanded a submarine unlike any the Navy had built before — one fast enough to keep up with a fleet steaming at 20 knots, long-ranged enough to cross the Pacific without refuelling, and heavily armed enough to sink a warship or a convoy on its own.

The submarines of the 1920s and early 1930s had failed on one or more of those counts, and the Navy’s Bureau of Ships spent the second half of the 1930s working out, boat by boat, what a fleet submarine should be.

From Tambor to Gato

The Gato was the direct successor of the Tambor class, of which twelve boats were built in 1939–1940. The Tambor had shown that the fleet-submarine concept worked, but it had also shown its limits: its engines were unreliable, its internal layout was cramped, and its diving depth was limited.

The Gato kept the Tambor‘s hull form and general arrangement but fitted more reliable diesel engines — General Motors, Fairbanks-Morse, and Hooven-Owens-Rentschler units, depending on the yard — improved the air-conditioning and the crew’s living spaces, and increased the torpedo load. The first Gato, USS Gato (SS-212) herself, was laid down at Electric Boat in Groton, Connecticut, in October 1940 and commissioned in December 1941, only weeks after Pearl Harbor.

The class was built at four yards — Electric Boat, Portsmouth, Mare Island and Manitowoc in Wisconsin, whose boats had to be floated down the Mississippi to reach the sea — and 77 boats were completed by 1944.

The torpedo crisis

The Gato’s early war was dominated by a weapon that did not work. The Mark 14 torpedo, the fleet submarine’s standard weapon, ran about 10 feet deeper than set, so that it passed under its target; its magnetic exploder, designed to detonate under a ship’s keel, often failed or exploded prematurely; and even when the magnetic exploder was switched off, the contact exploder sometimes failed on a square hit.

Submarine captains reported perfect attacks that produced no explosion, and the Bureau of Ordnance blamed the captains, accusing them of poor shooting. It was not until 1943, when tests at Pearl Harbor under Admiral Charles Lockwood proved the depth mechanism faulty and the exploders unreliable, that the faults were corrected.

By then the Gato boats had been fighting for eighteen months with a weapon they could not trust, and their sinking totals — modest in 1942, rising sharply in 1943 and 1944 — tell the story of a torpedo fixed at last.

4. Design

Hull and machinery

The Gato was 311 feet 9 inches long, with a beam of 27 feet 3 inches, and displaced about 1,525 tons on the surface and about 2,424 tons submerged. Four diesel engines, of 5,400 horsepower in total, drove the boat on the surface at about 20.25 knots and charged two large battery banks; submerged, four electric motors of 2,740 horsepower drove it at about 8.75 knots, and at 2 knots it could remain submerged for about 48 hours.

The boat’s range of about 11,000 nautical miles at 10 knots was the key to its role: it could sail from Pearl Harbor to the coast of Japan, patrol for weeks, and return without refuelling. The pressure hull was built of mild steel and tested to 300 feet, and in practice Gato crews often took their boats deeper — the hull was stronger than its rated depth, and the 100-foot margin that the later Balao class gained by using high-tensile steel was a refinement, not a revolution.

Armament and sensors

The Gato’s armament was the heaviest an American submarine had yet carried: ten 21-inch torpedo tubes — six forward and four aft — with 24 torpedoes, a 3-inch deck gun (later replaced by a 5-inch gun on many boats), and 20 mm and .50-calibre anti-aircraft guns. The six-tube bow salvo was the standard American attack, and the four stern tubes let the boat fire at a pursuer without turning.

The boat carried the SJ surface-search radar and the SD air-search radar, which by 1943 allowed it to find targets at night and to detect aircraft in time to dive. Radar changed the submarine war: it let Gato captains attack on the surface at night, when their boats were fastest, and it let them avoid the aircraft patrols that had been their greatest danger in 1942.

The crew of six officers and 54 enlisted men lived in conditions that were cramped but, by the standards of any other navy, comfortable — air-conditioned, with refrigeration and fresh-water distillers, and with bunks enough that only a few men had to share.

Life aboard and diving depth

Life aboard a Gato was hard in ways that have little to do with the enemy. The boat was hot and damp in the tropics, cold in the northern Pacific, and crowded everywhere: 60 men lived and worked in a steel tube 311 feet long, sharing bunks, eating in shifts, and going weeks without fresh air or sunlight.

Fresh water was rationed, showers were rare, and the smell of diesel, sweat and cooking filled every compartment. Yet the Gato was, by the standards of its time, a good boat to live in — far roomier than a German U-boat, with a proper galley, a small freezer, and bunks with mattresses rather than hammocks.

The 300-foot test depth was a paper figure: in combat, Gato crews routinely dived to 400 feet and more when depth charges were falling, and the hull held. The boat’s real limit was not its depth but its submerged speed — about 9 knots — which meant it had to attack from ahead, on the surface, or not at all.

5. Variants

Variant	Years	Key features	Numbers
Gato (fleet type)	1941–1944	Mild-steel hull, 300 ft test depth, 10 torpedo tubes, 3-in deck gun	77 completed
Gato (late war)	1943–1945	Cut-down conning tower, 5-in deck gun, improved radar	Many refitted
GUPPY conversions	1947–1952	Streamlined sail, snorkel, larger batteries, higher submerged speed	Several
Radar picket (SSR)	1950s	Large air-search radar, extended sail	Small numbers
Foreign transfers	1950s–1960s	Transferred to Argentina, Brazil, Greece, Italy, Japan, Spain, Turkey and others	Dozens

A single design, built at four yards

The Gato class was built to a single design, and the differences between boats were small: which yard built them, which diesel engines they received, and which gun and radar fittings they carried. Electric Boat at Groton built the most, Portsmouth and Mare Island built many, and Manitowoc in Wisconsin built boats that were floated down the Mississippi in a floating dry dock to reach the sea — a remarkable feat of logistics that delivered submarines from the middle of the American continent.

Late-war boats were fitted with a cut-down conning tower to reduce the silhouette, a 5-inch deck gun in place of the 3-inch, and improved SJ and SD radar. The class’s uniformity was a strength: a crew trained on one Gato could serve on any other, and a spare part made for one boat fitted them all.

Post-war modernisation

After the war, several Gato boats were modernised under the GUPPY programme — Greater Underwater Propulsion Power — which streamlined the hull, fitted a snorkel, and enlarged the batteries, raising submerged speed from about 9 knots to 15 or 16 knots. The GUPPY conversions were inspired by the German Type XXI U-boat, and they kept the Gato and Balao classes in front-line service into the 1950s and 1960s.

A smaller number were converted into radar picket submarines, carrying large air-search radars and acting as the eyes of a carrier task force. Others served as training boats, as test platforms for new sonars and torpedoes, and as reserve boats.

The class’s long post-war career, like the Balao’s, is a measure of how sound its basic design was: a hull laid down in 1940 could still be useful in 1960, because the hull itself had been right from the start.

Foreign service

Dozens of Gato boats were transferred to allied navies after the war, and they became the backbone of many smaller navies’ submarine forces. Argentina, Brazil, Greece, Italy, Spain and Turkey all operated Gatos, and Japan — the class’s wartime enemy — received two, which served in the post-war Japanese Maritime Self-Defense Force. The transfers spread American submarine practice and training around the world, and some boats remained in foreign service into the 1970s. The most remarkable foreign career belonged to the boats that served in the Turkish and Greek navies, where they patrolled the Aegean and the eastern Mediterranean through the Cold War, long after their American sisters had been retired to museums or scrapped.

The foreign Gato boats were not merely handed over and forgotten. The United States Navy trained their crews, supplied their spare parts, and shared its submarine doctrine with the navies that received them, so that a Turkish or Greek Gato crew in the 1960s fought, in many respects, as an American crew had fought in 1944. The transfers were, in that sense, an export of a way of war as much as an export of steel, and they shaped the submarine forces of a dozen navies for a generation.

6. Operational History

The first year: learning to fight

The Gato boats entered the war in the worst possible circumstances. In 1942, American submarines were few, their torpedoes did not work, and the Japanese had not yet been forced to convoy their shipping — but they were also not yet hunting submarines systematically.

Gato captains learned their trade the hard way, in patrols that often ended with no sinkings at all, and with depth-charge attacks that taught them how deep their boats could go and how quiet they had to be. The turning point came in 1943, when the torpedo faults were corrected and when Admiral Lockwood, commanding submarines in the Pacific, gave his captains a simple order: be aggressive, attack on the surface at night, and close to short range.

The sinking totals rose at once, and the Gato class, which had been the instrument of the first year’s frustration, became the instrument of the campaign that followed.

Wahoo, Growler and Harder

USS Wahoo under Dudley Morton

USS Wahoo (SS-238), commanded by Lieutenant Commander Dudley Morton, was the most aggressive submarine of the early war and the model for the captains who followed. In five patrols in 1943, Wahoo sank about 20 ships totalling more than 60,000 tons, and Morton became famous for attacking on the surface, for fighting it out with escorts, and for a patrol in the Sea of Japan in which he sank several ships in a single day.

Morton and his executive officer, Richard O’Kane — who would later command Tang — made Wahoo the boat every young submarine officer wanted to serve on. In October 1943, on her seventh patrol, Wahoo was sunk in La Pérouse Strait by Japanese aircraft and escorts, with the loss of all 80 men aboard.

Her wreck was found in 2006, and Morton remains one of the most admired submarine commanders in American history.

USS Growler and USS Harder

USS Growler (SS-215), commanded by Lieutenant Commander Howard Gilmore, earned her fame in February 1943, when Gilmore, wounded on the bridge during a surface attack, ordered his crew to dive and leave him behind, saying “Take her down!” — words that became a legend in the submarine service. Gilmore received the Medal of Honor posthumously, and Growler fought on until she was lost in November 1944.

USS Harder (SS-257), commanded by Samuel Dealey, was the most successful Gato by tonnage in some counts, sinking about 16 ships including several Japanese destroyers — a remarkable feat, since destroyers were the fastest and hardest targets a submarine could attack. Dealey was lost with Harder in August 1944, and he too received the Medal of Honor.

The three boats — Wahoo, Growler and Harder — lost their captains and their crews, and their stories are the core of the Gato class’s legend.

Wolfpacks and the strangulation of Japan

By 1944, the Gato boats were fighting in wolfpacks — groups of three submarines, coordinated by radio, that attacked convoys together — and in the sea lanes that carried Japan’s oil, food and raw materials. The submarine campaign’s results were decisive: in 1944 alone, American submarines sank more than 1.5 million tons of Japanese shipping, and by 1945 Japan’s merchant fleet had been reduced to a fraction of its pre-war size.

The Gato boats shared in that success, and USS Flasher (SS-249) became the most successful Gato by tonnage, credited with about 100,000 tons sunk. The class also sank Japanese warships, including the aircraft carrier Taiyo (by USS Rasher) and the cruiser Atago (by USS Darter), and it carried out special missions — landing coastwatchers and guerrillas in the Philippines, rescuing downed airmen, and photographing enemy-held beaches before invasions.

The submarine force’s contribution to the Pacific war, of which the Gato was the largest part, was second only to the carrier force itself.

Losses and cost

Twenty Gato-class boats were lost in the war — more than a quarter of the class — with the loss of about 1,500 men. The losses included Wahoo, Growler, Harder, Darter (scuttled after running aground), Tang‘s predecessor in spirit if not in class, and many boats whose fate is still unknown, lost to mines or to Japanese aircraft or escorts in waters where no witness survived.

The United States Navy lost 52 submarines in the Second World War, with the loss of about 3,500 submariners — the highest casualty rate of any branch of the American armed forces, at about 22 per cent. The Gato’s record is therefore a record of both remarkable success and remarkable sacrifice, and the class is remembered in the submarine service not only for the ships it sank but for the men it lost.

7. Performance and Specifications

Specifications in full

The figures in the table below are the standard Gato-class figures, taken from the Navy’s design data and from the boats as completed. Displacement, speed and range varied slightly from boat to boat, because the four building yards fitted different diesel engines and because wartime additions — radar, extra guns, and the cut-down conning tower — changed the weight and the silhouette of the later boats.

The test depth of 300 feet was the figure the Navy guaranteed, not the limit of what the boats could do: in combat, Gato captains regularly took their boats to 400 feet or more when depth charges were falling, and the mild-steel hull held.

The range figure of about 11,000 nautical miles was the reason the class could patrol from Pearl Harbor to the coast of Japan and back without refuelling, and the torpedo load of 24 weapons, fired from ten tubes, was the reason a single boat could attack a convoy more than once.

Specification	Gato class
Displacement (surfaced)	About 1,525 tons
Displacement (submerged)	About 2,424 tons
Length	311 ft 9 in (95.0 m)
Beam	27 ft 3 in (8.3 m)
Test depth	300 ft (91 m)
Surface speed	About 20.25 knots
Submerged speed	About 8.75 knots
Surface range	About 11,000 nautical miles at 10 knots
Submerged endurance	About 48 hours at 2 knots
Torpedo tubes	10 × 21 in (6 bow, 4 stern)
Torpedoes carried	24
Deck gun	1 × 3-in (later 5-in)
Crew	6 officers, 54 enlisted
Boats completed	77

Comparison with other submarines

Compared with the German Type VII U-boat, the Gato was much larger, longer-ranged and more heavily armed: a Type VII displaced about 770 tons surfaced, carried 14 torpedoes and had a range of about 8,500 nautical miles, against the Gato’s 1,525 tons, 24 torpedoes and 11,000 nautical miles. Compared with the Japanese I-class submarines, the Gato was faster on the surface, better equipped with radar, and far more numerous.

Its one weakness, shared with every fleet submarine of its generation, was its submerged speed: at about 9 knots submerged, it could not keep up with a fast convoy once it had dived, and it had to attack from ahead, on the surface, or not at all.

That weakness was only corrected after the war, by the GUPPY conversions, and it was not fully corrected until the nuclear submarine made submerged speed irrelevant. In its own time, however, the Gato was the best-balanced fleet submarine in the world, and its balance of range, armament, habitability and survivability is the reason it was built in such numbers and then improved, rather than replaced, in the Balao class.

8. Operators

The United States Navy

The Gato class was built for the United States Navy, which operated all 77 boats during the war and kept the class in service long after the war ended. In American hands the boats served first as fleet submarines, then as GUPPY conversions in the Cold War, and finally as training boats, test platforms and reserve boats, training new generations of submariners in the skills the wartime crews had learned the hard way.

The Navy’s submarine schools at Groton and Pearl Harbor used Gato boats to teach diving, torpedo firing and damage control, and the boats’ roomy, well-laid-out interiors made them good classrooms. The last American Gato in commission, USS Cod (SS-224), was not decommissioned until 1971, thirty years after the class had entered service.

Allied and foreign navies

Dozens of Gato boats were transferred to allied navies after the war, and they became the backbone of many smaller navies’ submarine forces. Argentina, Brazil, Greece, Italy, Spain and Turkey all operated Gatos, and Japan received two, which served in the post-war Japanese Maritime Self-Defense Force. The transfers spread American submarine practice and training around the world, and some boats remained in foreign service into the 1970s.

The most remarkable foreign career belonged to the boats that served in the Turkish and Greek navies, where they patrolled the Aegean and the eastern Mediterranean through the Cold War, long after their American sisters had been retired to museums or scrapped — a second life that the class’s designers, in 1940, could never have imagined.

9. Legacy and Influence

The boat that proved the fleet submarine

The Gato’s legacy is the American submarine force itself. The class proved that the fleet-submarine concept worked — that a submarine could be fast enough, long-ranged enough and heavily armed enough to fight a war across the Pacific — and it proved it in combat, under the worst conditions, with a faulty torpedo and against an enemy that learned quickly.

The campaign the Gato boats fought became the model for American submarine doctrine in the Cold War, and the boats’ success proved that the submarine, used systematically against merchant shipping, could be a decisive weapon of war. The Balao class, which followed the Gato, was not a new design but a Gato with a stronger hull, and that fact is the best measure of how right the Gato’s design had been.

The human legacy

The Gato also left a human legacy. The submarine service’s culture — small crews, high standards, aggressive commanders, and a willingness to take risks that other branches would not — was forged in the Gato boats of 1942 to 1944, and it survives in the American submarine force today.

The names of the Gato boats — Wahoo, Growler, Harder, Flasher, Darter — are still remembered in the submarine force, and the lessons of their patrols are still taught to young officers. The words of Howard Gilmore — “Take her down!” — are still quoted in the submarine service, and the loss of twenty Gato boats and about 1,500 men is still remembered at the submarine memorials at Pearl Harbor and Groton.

The class’s memorials remember the men as much as the boats, and the Gato’s place in that story is central: it was the boat that carried the submarine war through its hardest year.

10. Surviving Examples

Museum ships in the United States

Several Gato-class boats survive as museum ships, and they are among the best-preserved Second World War submarines in the world. USS Cod (SS-224) is preserved at Cleveland, Ohio, where she is maintained in working order and open to visitors. USS Silversides (SS-236) is preserved at Muskegon, Michigan. USS Drum (SS-228) is preserved at Mobile, Alabama, alongside the battleship USS Alabama.

USS Cavalla (SS-244) is preserved at Galveston, Texas, and USS Pampanito (SS-383) — a Balao, often displayed with the Gato story — is preserved at San Francisco. These boats are maintained by volunteers and by museum staff, and walking through their narrow passageways, past the torpedo tubes and the bunks and the control room, gives a visitor a clearer sense of submarine life than any book can. Cod, in particular, is kept in remarkable condition, with her engines still able to run.

Survivors abroad and visiting them

Outside the United States, the former USS Gato boats that served in foreign navies have mostly been scrapped, but their memory survives in the navies they served — in Turkey, Greece, Argentina and Brazil, where the boats trained generations of submariners who went on to serve in modern submarines.

For anyone who wants to understand what life was like aboard a Second World War submarine, a visit to Cod at Cleveland or Drum at Mobile is the best introduction there is, because both boats are preserved in the places where the submarine war was remembered, and both are kept in a condition that lets a visitor see, touch and smell the world their crews lived in.

The Gato boats that survive are not merely exhibits; they are the last witnesses of the submarine campaign that strangled Japan.

Frequently Asked Questions

What is the Gato-class submarine?
The Gato class was the United States Navy’s first mass-produced fleet submarine. 77 boats were built between 1940 and 1944, with a range of about 11,000 nautical miles, 10 torpedo tubes and a 3-inch deck gun.

How is the Gato different from the Balao class?
The Gato and the Balao shared the same hull form, machinery and armament, but the Balao’s pressure hull was built from high-tensile steel instead of mild steel, raising the test depth from 300 feet to 400 feet.

How many Gato-class submarines were built?
77 Gato-class boats were completed between 1940 and 1944, at four yards: Electric Boat, Portsmouth, Mare Island and Manitowoc.

Which Gato was the most successful?
USS Flasher (SS-249) was the most successful Gato by tonnage, credited with about 100,000 tons sunk. USS Wahoo and USS Harder were the most famous, for the aggression of their commanders.

What happened to USS Wahoo?
USS Wahoo, commanded by Dudley Morton, was sunk in La Pérouse Strait in October 1943 by Japanese aircraft and escorts, with the loss of all 80 men aboard. Her wreck was found in 2006.

Where can I see a Gato-class submarine today?
USS Cod at Cleveland, Ohio, USS Silversides at Muskegon, Michigan, and USS Drum at Mobile, Alabama, are all preserved as museum ships and open to visitors.

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• Balao-class Submarine

Sources

1. Wikipedia, “Gato-class submarine” — production of 77 boats, specifications, test depth of 300 feet, Wahoo, Growler and Harder.
2. Norman Friedman, U.S. Submarines Through 1945: An Illustrated Design History (Naval Institute Press, 1995) — design, Tambor to Gato, and GUPPY conversions.
3. Clay Blair, Silent Victory: The U.S. Submarine War Against Japan (J. B. Lippincott, 1975) — the submarine campaign, tonnage figures and patrol history.
4. Naval History and Heritage Command, “Gato (SS-212)” and Wahoo (SS-238) histories — commissioning, patrols and losses.
5. Richard O’Kane, Wahoo: The Patrols of America’s Most Famous World War II Submarine (Presidio Press, 1987) — Morton’s patrols and the loss of Wahoo.
6. Theodore Roscoe, United States Submarine Operations in World War II (Naval Institute Press, 1949) — operations, wolfpacks and special missions.