Do US Navy Submarines Have Two Propellers?

The question of whether US Navy submarines have two propellers is an intriguing one. This article delves into the history and current state of submarine propulsion in the United States Navy, focusing on the use and design of multiple propellers.

Historical and Current Trends in Propulsion

Historically, US Navy submarines have relied on a single propeller for their primary forward movement. This was the case for the majority of operational subs, save for a few exceptions. For instance, the last operational USN submarine to use two propellers for normal forward movement was the USS Swordfish (SSN-579), which was decommissioned in 1989. Before that, the Halibut (SSGN-587), laid down in 1957 and decommissioned in 1976, was the last twin-screw operational submarine.

[Edit - Thanks to Michael McHale for pointing out that USS Jack (SSN-605) played a key role in this discussion. Jack, a modified Permit-class boat laid down in 1960, launched in 1963, and decommissioned in 1990, had a similar dual concentric prop arrangement to the Albacore. The modifications to Albacore were designed in 1962 and completed in 1963, making Jack the more recent addition to the discussion. Specifically, Jack had many reliability issues due to the complexity of its dual spool counter-rotating turbines and the associated seals. While her seal worked, it was only effective at a 600-foot test depth, unlike the Permit-class submarines, which had a test depth of 1300 feet. A single-shaft turbine with reduction gears might have been a better choice at the time, but gear noise could have been a concern. Albacore’s seal worked well up to 600 feet, but it's assumed that Jack was designed to reach 1300 feet, a test depth higher than that of the Permit-class submarines.

End Edit]

The Unique Case of USS Albacore

USS Albacore (AGSS-569), although not operational, is notable for its experimental use of two coaxial counter-rotating propellers. Decommissioned in 1972, Albacore is the only USN submarine to have utilized this arrangement. Currently, Albacore is on display, making its propeller configuration more accessible for study and display.

Secondary Propulsive Units

While the main propulsion system is designed for high-speed operation, US Navy submarines also have a smaller secondary propulsive unit. This unit is used for docking maneuvers and low-speed operations when the main propulsion system is not in use. This dual system ensures that the submarine can operate efficiently in a variety of scenarios.

In conclusion, while two main propellers were a feature of some earlier U.S. Navy submarines, the current trend is towards single propeller designs. However, the inclusion of a secondary propeller for specific tasks has ensured that the US Navy submarines remain adaptable and capable in a wide range of operational environments.

Further Reading:

Historical records of decommissioned submarines in the U.S. Navy Technical manuals of experimental submarine designs Interviews with submarine engineers and operators