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The Greater Underwater Propulsion Power Program (GUPPP) was initiated by the United States Navy after World War II. Like all programs in the military, some sort of "name" needed to be applied that would attract and hold attention. Since GUPPP didn't sound quite right, the third P was dropped and a Y added. Thus the word GUPPY, which had a far better ring to it since it did in fact sound more like a fish. At this time all submarines were named after undersea life.

The GUPPY was an extensive conversion that gave fleet boats a snorkel, a more streamlined hull, much greater battery capacity, and a BQR 2. There were a total of 50 GUPPY conversions made between 1946 and 1960. The GUPPYs were the best that the submarine force could do and still maintain a reasonable force structure. They had improved ASW capabilities and were far more survivable than standard World War II fleet boats, but reflected the limits of both money and technology, particularly before Korea and the two nuclear revolutions.

The WWII "fleet boat" submarines were basically surface ships that could submerge, but had very high drag when submerged. The fairing of hull and appendages led to the Guppy Class. This series forced designers to determine ways of minimizing drag while still achieving effective high speeds. Deck guns were removed, the outer hull was streamlined, the conning tower replaced by a sail, replaced the propellers, installed more air conditioning, and the battery capacity doubled. The program was successful, the converted submarines were capable of 18.2 kts submerged, exceeding their surfaced speed by 0.4 kts.

The Navy quickly combined German innovation with American engineering and design in boats with greater underwater propulsive power (for example the GUPPY 1 conversions) and the new Tang (SS-563) class. These boats demonstrated the possibilities and challenges of much greater submerged speed and prolonged submergence. Greater depth, speed, and personnel endurance became absolutely critical to the future.

The Navy began the program by reverse-engineering two captured Type XXI U-boats: U-2513 and U-3008. That analysis led to four goals: increase the submarines' battery capacities, streamline the boats' structures, add snorkels, and improve the fire control systems. The Tang class The Tang class of submarines was a product of the Greater Underwater Propulsion Power Program (GUPPY), which incorporated German U-boat technology into the United States Navy's submarine design. They comprised the state of the art in post-World War II conventionally-powered submarine design; a design that was incorporated into and replaced by the nuclear-powered submarines of the 1950s and beyond.

The Tang class was designed to incorporate these improvements, and proved to be so much better than the existing Gato-, Balao- and Tench-classes that the Navy decided to upgrade the existing fleet as well as build new boats. Those upgrades proceeded in seven variants: Fleet Snorkel, GUPPY I, GUPPY II, GUPPY IA, GUPPY IIA, GUPPY IB, and GUPPY III. (The apparently out-of-order sequence is correct). Some boats that went through an early phase were then upgraded further in a later phase.

Fleet Snorkel Program

The Fleet Snorkel boats were simply fleet boats with added snorkel induction and exhaust piping and masts. They also had their deck guns removed and sonar electronics installed where the gun magazine had been, but few or none of the other GUPPY modifications. These modifications were intended as an austere and less expensive alternative to GUPPY. Within two years of the end of the war, the U.S. Navy had a functional snorkel mast on an operational, high speed submarine- the Irex (SS 482).

During World War II German submarine losses increased sharply as radar-equipped Allied aircraft attacked U-boats running on the surface recharging their batteries. To charge the batteries that powered the electric motors for submerged operations, all submarines had to surface to run their air-breathing diesel engines. To counter the Allied radar threat the Germans perfected a Dutch device known as the snorkel. Using a snorkel a submarine could run its diesel engines and recharge its batteries while operating just below the surface. Air for the diesel engines was drawn into the submarine through the snorkel that was extended to the surface. To some extent the snorkel reduced vulnerability to detection and attack, but it protruded above the surface and could be detected by radar. The Germans introduced the snorkel too late in the war to make a difference.

The snorkel became a standard fixture of all diesel-electric submarines. Developed in its modern form by Germany in World War II, it was widely adopted and improved after the war. Basically, the snorkel connects a submerged submarine's diesels to the atmosphere through a pair of tubes, one for air intake, one for exhaust. A key feature is the head-valve on top of the air-intake mast that prevents water from entering. Before the snorkel, submarines had to surface to run their air-breathing diesel engines, but snorkel-equipped submarines can remain submerged, with only the tip of a mast exposed above the water for the required air.

GUPPY I Program

The external changes made by the first phase of the GUPPY program in 1947 improved streamlining of the bridge and shears structures, and periscope and radar mast supports. Deck guns and their associated containers were removed. All capstans, cleats, and rail stanchion supports were redesigned so that all deck fittings could be retracted or removed when rigged for dive. Most notably, the surface-ship-like sharp V-shaped "fleet boat bow" was replaced with a distinctive rounded "guppy bow" (which housed sonar hydrophones in a "chin mount"), and an SV-radar screen was added to the top of the sail, creating a distinctive side bulge.

These modifications changed not only the boats themselves but also their terminology: after a GUPPY conversion, the faired structure around the boat's conning tower and mast supports was called the "sail."

The internal changes made by the first phase of the GUPPY program were intended to improve electrical power, and included a new design of battery with more and thinner plates that would generate higher current for a longer time. However, these batteries had a shorter lives, took longer to charge, and required cooling water to the battery terminals and termination bars. Four 126-cell batteries were installed in each boat: two in the after battery well, one-and-a-half in the lower level of the forward battery well, and the remaining half in the forward end of the pump room. These four batteries could be connected in series or parallel, providing a wide range of voltages and currents, and thus a wide range of speeds.

In the engine room, two or four of the earlier high-speed motors and reduction gears were replaced by slow-speed motors. All open-front switchboards were replaced with enclosed splash-proof cabinets. Lighting and other "hotel" electical loads were converted to use 120-volt 60-hertz alternating current, and ship electronics to use 120-volt 400-hertz AC.

With the deck gun removed, the ammunition magazine under the galley was no longer useful, and was replaced by sonar electronics.

GUPPY II Program

The GUPPY II conversion, from 1947 to 1951, was generally similar to the GUPPY I except for the sail. The addition of three new masts -- snorkel induction, snorkel exhaust, and ESM mast -- required more room in the upper portion of the sail to support the new masts. The Bureau of Ships approved two different sail designs: The "Electric Boat Sail" had a straight trailing edge, round windows, a wider top and a more rounded forward edge. The "Portsmouth Sail" had a thinner top, curved trailing edge, square windows and a sharper lower forward edge. It was put on all boats which used the government plans for the conversion. Some boats with a Portsmouth Sail had an SV-radar and needed extra room to house the screen, thus had a bulge at the sail top. Later modifications put the SS or SS2 radars on these and other boats which had a smaller screen and had an indicator with interlocks which allowed the mast to be housed only with the screen in certain angular positions.

Also, some GUPPY II and GUPPY III boats had their sails extended higher above the waterline, the "Northern Sail," to raise the bridge, allowing it to be manned in more severe weather.

All boats converted during the GUPPY II program that originally had high-speed drive motors with reduction gears had these replaced with low-speed direct-drive motors, producing 2500 horsepower per shaft. The battery wells were enlarged to accept 504 GUPPY cells in four batteries. The boats had their bows replaced and the entire superstructure streamlined.

GUPPY IA Program

Because of the expense of the GUPPY II program, the GUPPY IA program of 1951 provided an interim measure that included the less-expensive changes, but not the drastic modifications performed on the GUPPY IIs.


Running from 1952 through 1954, GUPPY IIA streamlined the boat, installed a new sail, a guppy bow, and new motors where necessary, just as GUPPY II did. IIA, however replace one forward engine with air-conditioning plants and refrigeration units. Some boats had the high-pressure air compressors relocated to the lower level of the forward engine room. The chill box and freeze boxes were moved to the forward end of the after battery under the galley. Sonar was moved to the space now available in the forward end of the pump room. GUPPY IIA boats had the same outward appearance as GUPPY II, except the IIA had only three diesel exhaust outlets and the II had four.

GUPPY IB Program

The GUPPY IB program, from 1953 to 1955, was another interim conversion that converted four boats for transfer to foreign navies. These boats had snorkels and were somewhat like the GUPPY IA except that they were not equipped with the modern sonar, fire control systems, or ESM.


A problem that became evident in the mid-1950s operations was the increasing amount of electronic equipment that was required on a submarine. The ESM equipment, the sonar equipment and the new fire control computer took up a lot of space. Certain boats, which already had the majority of the Guppy conversion work done (already Guppy II) and were in decent condition, were taken into the shipyard from 1959 to 1963, cut in half and lengthened with a new 15 foot section. The extension was in the forward end of the control room and created a new space for sonar. (TIRU was only lengthened 12.5 feet instead of 15.) The Conning Tower was renewed with an attitional 5 foot section to accomodate the Mk 101 fire control system and Mk 37 director. The Guppy III conversion was accomplished as a part of the Fleet Rehabilitation and Modernization (FRAM) program. These four-battery, four-engine boats became Guppy III. The "Northern Sail" was also added, as it was on other classes of Guppys, in order to get the bridge higher which allowed it to be manned in severe weather. TIRU retained its three engine arrangement.

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Page last modified: 22-07-2011 17:39:36 ZULU