USS Diodon conversion to GUPPY II
Since 09-09-05
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.
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
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