Greater Underwater Propulsion Power Program
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The Greater Underwater Propulsion Power Program (GUPPY) was initiated by the United States Navy after World War II to improve the submerged speed, maneuverability, and endurance of its submarines. (The 'Y' in the acronym was added to increase pronouncability.)
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 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; see below.) Some boats that went through an early phase were then upgraded further in a later phase.
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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.
Fleet Snorkel Boats
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 I Boats
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 (1.9 MW) 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 II Boats
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.
GUPPY IA Boats
GUPPY IIA Program
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 IIA Boats
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.
GUPPY IB Boats
- Barb (SS-220) (became ITNS Enrico Tazzoli (S-511) of the Marina Militare)
- Dace (SS-247) (became ITNS Leonardo da Vinci (S-510) of the Marina Militare)
- Hawkbill (SS-366) (became HNLMS Zeeleeuw (S-803) of the Royal Netherlands Navy)
- Icefish (SS-367) (became HNLMS Walrus (S-802) of the Royal Netherlands Navy)
- Jallao (SS-368) (became SPS Narciso Monturiol (S-35) of the Spanish Navy)
GUPPY III Program
In the mid-1950s, the increasing amount of electronic equipment required on a submarine — ESM equipment, sonar equipment, fire control computer — was recognized as a problem. From 1959 to 1963, this problem was addressed by selecting boats that already had completed most GUPPY II conversion work and were in good condition, cutting them in half, and adding a 15 foot (4.6 m) section forward of the control room to create room for new sonar equipment. Tiru (SS-416) was only lengthened 12.5 feet (3.8 m) instead of 15 ft (4.6 m) The conning tower in the sail gained additional five foot (1.5 m) section to accommodate the Mk 101 fire control system and Mk 37 director. The GUPPY III conversion was part of the Fleet Rehabilitation and Modernization (FRAM) program.
GUPPY III Boats
- Clamagore (SS-343)
- Cobbler (SS-344)
- Corporal (SS-346)
- Greenfish (SS-351)
- Tiru (SS-416)
- Trumpetfish (SS-425)
- Remora (SS-487)
- Volador (SS-490)
- Pickerel (SS-524)