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 pronounceability.)
The Navy began the program by testing and reverse engineering two captured Type XXI U-boats: U-2513 and U-3008. That analysis led to four goals: increasing the submarines' battery capacity, streamlining the boats' structures, adding snorkels, and improving fire control systems. The Navy immediately focused on designing a new class of submarines, but the Bureau of Ships believed that the vast fleet of existing Gato, Balao, and Tench class submarines could be converted to incorporate the desired improvements. The initial two boat test program, implemented by the Portsmouth Naval Shipyard, eventually grew into several successive conversion programs. Those upgrades proceeded in seven variants: GUPPY I, GUPPY II, GUPPY IA, Fleet Snorkel, 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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GUPPY I Program
The prototype GUPPY boats appeared in 1947. Externally, they featured improved streamlining of the bridge and shears structures, and periscope and radar mast supports. Deck guns and their associated containers were removed. An SV-radar screen was added to the top of the sail, creating a distinctive side bulge. All capstans, cleats, and rail stanchion supports were redesigned so that they could be retracted or removed when rigged for dive. Most notably, the sharp V-shaped "fleet boat bow" was replaced with a distinctive rounded "Guppy bow" (which housed sonar hydrophones in a "chin mount").
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."
Internally, the boats underwent considerable rearrangment to accommodate englarged battery wells and batteries of greatly increased electrical power. The batteries themselves were of 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 life, 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" electrical 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.
In service, these boats offered massively improved underwater performance, reaching speeds as high as 18 knots.
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
Due to the expense of the GUPPY II program, the Bureau of Ships devised the GUPPY IA program of 1951 as a cheaper alternative. The GUPPY IA conversion included most features of the GUPPY II, with the exception of the four-cell GUPPY battery configuration. Instead, the GUPPY IA retained the two original battery wells, fitted with more powerful Sargo II batteries. These batteries featured electrolyte agitation, battery cooling, and open tank ventilation. The sonar room was relocated from the forward torpedo room to a space under the galley.
GUPPY IA Boats
Fleet Snorkel Program
When the Navy realized that it would not be able to fund all the GUPPY conversions it desired, it devised the Fleet Snorkel program as a means of adding the minimum necessary modifications to fleet boats. The Fleet Snorkel modernization added a streamlined sail and snorkel. A higher capacity air-conditioning system and electrical system were also installed. The deck guns and auxiliary diesel were removed. Unlike the GUPPY conversions, the Fleet Snorkel boats retained their original deck structure, bow, and storage batteries. Despite their limited features, the Fleet Snorkel boats served almost as long as the more modern GUPPY boats.
Fleet Snorkel Boats
GUPPY IIA Program
Running from 1952 through 1954, the GUPPY IIA conversion was very similar to the preceding GUPPY IA. The boats retained the Sargo II battery configuration. The GUPPY IIA, however, alleviated the cramped internal conditions of earlier conversions by removing one forward engine and replacing it 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. The sonar room was relocated to the space now available in the forward end of the pump room. GUPPY IIA boats had the same outward appearance as the GUPPY II and IA, except the IIA had only three diesel exhaust outlets, while the earlier conversions had four.
GUPPY IIA Boats
GUPPY IB Program
GUPPY IB was an informal designation for a limited upgrade and modernization given to four boats for transfer to foreign navies. These boats had snorkels and were generally similar to the GUPPY IA except that they were not equipped with the modern sonar, fire control systems, or ESM. The two Italian boats were of the thin-skinned Gato class.
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)
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 GUPPY II boats that were in good condition, cutting them in half, and adding a 15 foot (4.6 m) section forward of the control room to create space for a new sonar room, berthing, and storerooms. Tiru (SS-416), the first conversion, differed from subsequent boats. She was only lengthened 12.5 feet (3.8 m) instead of 15 ft (4.6 m), and had one engine removed.
All boats received the PUFFS passive ranging sonar, identifiable by the three fin-like sonar domes added to the superstructure. The conning tower in the sail gained an 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. All 24 GUPPY II boats were originally slated for GUPPY III upgrades, but budgetary constraints limited the program to nine boats.
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)