Few but Deadly: Meet the U.S. Navy’s Seawolf-Class Submarines

 In EPC, Sea, Forces & Capabilities

Key point These sub­marines are deadly and also very, very quite. They have been used to spy on America’s rivals since their con­struc­tion.

The Seawolf-class sub­marines were envi­sioned as the best sub­marines ever built. Designed to suc­ceed the Los Angeles – class attack sub­marines and main­tain America’s edge in the under­wa­ter domain, the class suf­fered from cost over­runs and the col­lapse of the Soviet Union. While still some of the best sub­marines ever built, they were built at reduced num­bers. In many respects, they are the F‑22 of sub­marines: widely con­sid­ered the world’s best, but costs made wide their wide usage a major chal­lenge. 

This first appeared in 2017 and is being repost­ed due to reader inter­est.

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In the late 1980s, the U.S. Navy was faced with a crisis. In 1980, the Soviet Union had received information from the Walker family spy ring that the Navy could track its sub­marines through exces­sive pro­peller noise. As a result, the Soviet Union went look­ing for advanced Western machin­ery to make better pro­pellers. In 1981, the Japanese com­pa­ny Toshiba sold pro­peller milling machin­ery — now rel­a­tive­ly common nine-axis CNC milling machines — to the Soviet Union via the Norwegian Kongsberg cor­po­ra­tion.

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By the mid 1980s, the Soviet Union’s new machin­ery began to make itself felt. The new Akula-class sub­marines had a “steep drop in broadband acoustic noise profiles”. One gov­ern­ment source told the Los Angeles Times, “the sub­marines start­ed to get silent only after the Toshiba stuff went in.” On top of run­ning silent, the Akula class could dive to depths of up to two thou­sand feet — while the U.S. Navy’s front­line sub­marines, the Los Angeles class, could dive to only 650 feet.

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To combat the threat of the Akula class, the U.S. Navy respond­ed with the Seawolf class of nuclear attack sub­marines. The Seawolf sub­marines were designed with HY-100 steel alloy hulls two inches thick, the better to with­stand the pres­sures of deep diving. HY-100 steel is rough­ly 20 percent stronger than the HY-80 used in the Los Angeles class. As a result, the sub­marines are capa­ble of diving to depths of up to two thou­sand feet, and crush depth esti­mates run from 2,400 to 3,000 feet.

At 353 feet, Seawolf subs were designed to be slight­ly short­er than their pre­de­ces­sors, by just seven feet, but with a twenty per­cent wider beam, making them forty feet wide. This width made them sub­stan­tial­ly heav­ier than the subs before them, top­ping the scales at 12,158 tons sub­merged.

The Seawolf sub­marines are each pow­ered by one Westinghouse S6W nuclear reac­tor, dri­ving two steam tur­bines to a total of 52,000 shaft horse­pow­er. The class was the first class of American sub­ma­rine to uti­lize pump-jet propul­sors over pro­pellers, a fea­ture that has car­ried over to the newest Virginia class. As a result, a Seawolf is capa­ble of eigh­teen knots on the sur­face, a max­i­mum speed of 35 knots under­wa­ter, and a silent run­ning speed of about 20 knots.

The Seawolf class is equipped with the BQQ 5D sonar system, which fea­tures a twenty-four-foot-diameter bow-mount­ed spher­i­cal active and pas­sive array as well as wide-aper­ture pas­sive flank arrays. The sub­marines are being refit­ted with TB-29A thin-line towed array sonar systems. Rounding out sonar sys­tems is the BQS 24, for detec­tion of close-range objects such as mines.

The ship’s orig­i­nal combat data system was the Lockheed Martin BSY‑2, which uses a net­work of sev­en­ty Motorola 68030 proces­sors — the same proces­sor that drove early Macintosh com­put­ers — and is now being replaced with the AN/BYG‑1 Weapons Control System.

The sub­marines were designed to be true hunters, and as a result have eight tor­pe­do tubes, double the number of ear­li­er sub­marines. It has stores for up a com­bi­na­tion of up to fifty Mark 48 heavy­weight tor­pe­does, Sub-Harpoon anti­ship mis­siles, and Tomahawk mis­siles. Alternatively, it can sub­sti­tute some of this ord­nance for mines.

The result­ing sub­ma­rine is accord­ing to the U.S. Navy ten times qui­eter over the full range of oper­at­ing speeds than the Improved Los Angeles sub­marines, and an aston­ish­ing sev­en­ty times qui­eter than the orig­i­nal Los Angeles – class sub­marines. It can run quiet at twice the speed of pre­vi­ous boats.

This for­mi­da­ble increase in per­for­mance came at for­mi­da­ble increase in cost. The total Seawolf pro­gram was esti­mat­ed at $33 bil­lion for twelve sub­marines, an unac­cept­able cost con­sid­er­ing the Soviet Union — and the threat of the Akula and follow-on subs — ended in 1991. The pro­gram was trimmed to just three sub­marines that cost $7.3 bil­lion.

The extreme quiet­ness of the Seawolf class gave the Navy the idea of mod­i­fy­ing the last sub­ma­rine, USS Jimmy Carter, to sup­port clan­des­tine oper­a­tions. An extra one hun­dred feet was added to the hull, a sec­tion known as the Multi-Mission Platform (MMP). The MMP gives Carter the abil­i­ty to send and recov­er Remotely Operated Vehicles/Unmanned Underwater Vehicles and SEALs and diving teams while sub­merged. It includes berthing for up to fifty SEALs or other attached per­son­nel. Carter also fea­tures aux­il­iary maneu­ver­ing devices fore and aft for pre­cise maneu­ver­ing in sit­u­a­tions such as under­sea cable tap­ping and other acts of espi­onage.

The Seawolf-class sub­marines are out­stand­ing sub­marines, but the Cold War mind­set at the time of devel­op­ment accept­ed high per­for­mance and con­se­quent­ly high costs to meet a high-level threat. The post – Cold War Virginia class forced the Navy to reign in costs while still pro­duc­ing a pro­gres­sive­ly better sub­ma­rine. While unsuc­cess­ful as a class, the tiny Seawolf fleet is still a very useful part of the U.S. Navy sub­ma­rine force, giving it capa­bil­i­ties not even the Virginia class can match.

Kyle Mizokami is a defense and nation­al secu­ri­ty writer based in San Francisco who has appeared in the Diplomat, Foreign Policy, War is Boring and the Daily Beast. In 2009 he cofound­ed the defense and secu­ri­ty blog Japan Security Watch. You can follow him on Twitter: @KyleMizokami. This first appeared in 2017 and is being repost­ed due to reader inter­est.

Image: Reuters

 

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