Greater Underwater Propulsion Power Program

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USS Greenfish after GUPPY III

The Greater Underwater Propulsion Power Program was a United States Navy program that aimed to modernize the submarine fleet after World War II. As Common acronym was Guppy elected; here the Y was used in place of the third P , so that the name, following the tradition of submarine naming, is based on an aquatic creature (in this case the guppy ). After this change, the name of the project will occasionally also mean Greater Underwater Propulsion Program Yet .

General

GUPPY was supposed to combine German submarine technology with American technology. In particular, two German submarines, U 2513 and U 3008 of class XXI were investigated using reverse engineering . The results of these investigations suggested that the battery capacity should be increased, the hull should be streamlined, the boats should be equipped with a snorkel and better fire control systems. The Tang class emerged from these specifications , and numerous older boats of the Gato , Balao and Tench classes were modernized.

At a time when the nuclear submarines were being developed and were on the rise in the US Navy, the old boats were just being modernized to bridge the period between World War I and serial production of nuclear submarines . This also explains why only a few new conventionally powered submarines were built after the World War. These were the Barracuda-class with three, the Sailfish-class with two, the Grayback-class with two and the Barbel-class with three boats as well as the single ship USS Darter (SS-576) in the years 1951-1958.

Stages of modernization

Fleet Snorkel

The Fleet Snorkel Program equipped some boats with a snorkel so that they could go under diesel instead of having to turn up. In addition, the mandatory deck gun was removed, the former magazines were used to accommodate a sonar system. This was the smallest expansion stage, but also the most cost-effective.

GUPPY I

USS Piper (SS-409) after conversion with BQR-4A bow sonar

In the GUPPY-I boats, the gun and other superstructures on the deck were removed from 1947, and the bow was also rounded off for better diving properties. The tower was also made more streamlined. The former grenade magazine was used to set up sonar devices.

In addition, more powerful batteries were installed, two of the four motors were replaced with special slow-speed crawling motors. Only two prototypes were converted, a snorkel was not yet included in this package.

GUPPY II

GUPPY II received the GUPPY-I improvements between 1947 and 1951, but also a snorkel and an ESM mast . For this purpose, the tower was enlarged in the upper area.

GUPPY IA

In 1951, GUPPY IA was created as a small GUPPY II conversion. In order to save money, the battery arrangement has not been changed, which simplifies maintenance.

GUPPY IIA

GUPPY II was carried out here between 1952 and 1954, but one of the diesel engines was replaced by air conditioning and cooling rooms to improve conditions for the crews.

GUPPY IB

From 1953 to 1955, four boats in GUPPY IB were equipped for export to GUPPY IA, but were not equipped with modern SONAR and ESM electronics. Two boats went to the Marina Militare , two to the Koninklijke Marine .

GUPPY III

In the 1960s, some GUPPY II boats were further modernized. To do this, they were cut in half as part of Fleet Rehabilitation and Modernization and lengthened by 12.5 feet (3.8 m) to provide more space for electronic systems.

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