Attrition: Squeezing More Years Out Of Old SSNs

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November 29, 2021: As more Los Angeles class SSNs (nuclear attack subs) approach retirement, the U.S. Navy has been taking an inventory of critical systems on each sub to determine what the remaining useful life of each system is. In the past nuclear subs were generally retired when their nuclear reactors needed refueling, an expensive and time-consuming process that takes several years and costs nearly a billion dollars. Many of the retiring Los Angeles boats had three-to-ten years of reactor life left and have spent several years waiting for regular maintenance because of a general backlog in shipyard capacity for such work. That was considered something of a scandal but the navy used the waiting time to carry out this assessment. The examination of SSNs approaching replacement found many of them were capable of extended service after their scheduled maintenance was carried out. This process normally includes upgrades or replacement of systems that do not require a lot of time. The navy also found at least five Los Angeles boats that were worth another reactor refueling. All this is to solve an expected problem that will last for nearly a decade as more Los Angeles subs approach retirement age and production of the new Virginia-class subs catches up with replacement needs.

This problem was noted a decade ago because, after the Cold War ended in 1991, the U.S. Navy got Congress to agree that the United States required an SSN fleet of at least 48 boats. Since the 1990s, increased submarine construction by Russia and China means this minimal safe number of SSNs climbed to 55 and that created a problem. Because only two new American SSNs were built in the 1990s, the SSN force would drop to about 40, before recovering in the 2030s. The cause was the sharp cut in SSN construction in the 1990s, and that it takes over 5 years to build each new SSN. The older Los Angeles SSNs approaching the end of their useful lives (33 years) meant that the force of available SSNs was rapidly shrinking. The navy tried to reduce the shortage by speeding up construction of new Virginia class SSNs, extending the life of some Los Angeles class boats by a few years, and basing some SSNs in the Western Pacific (Guam) to shorten the time needed to get to where they are needed; the coast of China and Russia as the main Chinese sub base is on Hainan Island and Russia’s is north of Japan on the Kamchatka Peninsula.

By 2013 the navy received the tenth Virginia class SSN; the USS Minnesota (SSN 783). This sub arrived 11 months ahead of schedule and was the last of 10 Block II Virginias. In 2008, the navy got its fifth Virginia 8 months ahead of schedule and under budget as well. The Virginia’s are taking less time to build and their completion rate is generally increasing from one to two a year over the next decade.

The Virginias cost about $2.2 billion each. They displace 7,800 tons, are 114.9 meters (377 feet) long, and 10.36 meters (34 feet) wide. Top speed is over 50 kilometers an hour and max depth is more than 250 meters (over 800 feet). The Virginians are armed with Tomahawk cruise missiles (in 12 vertical launching tubes) and four 53.3 cm (21 inch) torpedo tubes that can fire MK 48 torpedoes or deploy naval mines.

More important are the large number of electronic systems carried. These make the Virginias more difficult to detect and much better at detecting what is out there, which enables these subs to be more effective at espionage and scouting. The electronics can also quickly detect and identify incoming torpedoes and rapidly use countermeasures. The passive (listen only) sonar system is backed by a huge library of sounds. Virginias are also designed to operate in shallow waters and carry a SEAL Delivery Vehicle (sort of a minisub for getting SEALs ashore) on the deck of the sub. With a dozen or so SEALs on board a Virginia will be carrying nearly 150 people.

Virginia’s nuclear reactors are the new type that does not have to be refueled, having sufficient nuclear material to last 33 years. The reactors generate enough heat to provide 40,000 horsepower, as well as ample electricity for all the electronics. The block II models used less costly construction techniques, while the 8 Block III boats will have some design changes and new technology.

By 2021 the Navy has twenty Virginias in service with 60 to 70 or more to eventually enter service, depending on how much money is available and how well the substantially improved Block 5 models do.

Each block of Virginias represents improvements, some of them substantial. There are currently five subclasses of Virginia, each identified by a Block number. There are four Block 1s, all in service by 2008. The six Block 2s were all delivered by 2013. Eight Block 3s were all in service by 2020 and there will be ten Block 4s, with three in service by 2021 and the rest by the mid-2020s. The ten Block 5s won’t all be in service until the early 2030s and future Blocks will be based on the larger and more heavily armed Block 5s.

The Navy currently expects to build at least 66 Virginias but the importance of the large and more heavily armed Block Vs may increase that to over 70 subs with most of those based on the Block 5. Blocks 1-4 of Virginia are all armed the same way but eight of the ten Block 5s have additional space to store and launch missiles and can carry 65 missiles and torpedoes, 75 percent more than earlier Virginias. This is accomplished by adding a VPM (Virginia Payload Module) to the current design. This adds 25.6 meters to the length of the sub and increases displacement to 10,400 tons. The VPM adds four more of the large launch tubes that can hold different sizes of missiles. For example, each of launch tubes can carry seven Tomahawk cruise missiles or a smaller number of new missile designs in development, like the hypersonic missile. Earlier Virginias already had older individual launch tubes forward of the sail (conning tower). The VPM is added behind the sail. The VPM design was not ready when the first block 5 began construction so the first two Block 5s will lack the VPM and be the same size as earlier Virginias. These two Block 5s will have all the other additional features common to all Block 5s. This includes improved electronics and sensors and it is believed that the passive sonar in these model Virginias have much longer and accurate detection ranges. The Block 5 will also receive a large number of other equipment upgrades.

The U.S. currently has three classes of SSN. Most are the still 6,900-ton Los Angeles-class SSNs. Of the 62 Los Angeles boats built, 28 are still in service, plus two used as moored training ships and 32 retired or in the process of retiring. These are armed with 4 53.3 cm torpedo tubes; they carry 26 weapons for those tubes (either the Mk 48 torpedoes or BGM-109 Tomahawk cruise missiles). The last 31 Los Angeles-class SSNs built added the Mk 45 vertical-launch system (VLS), which carries another twelve Tomahawks. If built today these late model Los Angeles class boats would cost about $1.5 billion each. The first of these entered service in 1976, and the last one in 1996. These boats can last 30-35 years before they must be retired or undergo extensive (over half a billion dollars’ worth) of refurbishment and refueling. This can take 4-5 years and will keep the sub going for another 10-15 years. The navy initially sought enough money from Congress to refurb some of the elderly Los Angeles class boats and prevent the SSN fleet from shrinking below 45 boats. Examining the boats awaiting retirement revealed that the situation was not as bad as originally thought.

The navy problem with the SSN shortage was partially cause by cancellation of all but three of the twenty-nine 9,000-ton Seawolf-class SSNs ordered to replace the Los Angeles boats. Seawolf proved too expensive, and that problem was one of the main reasons for the lack of new SSNs in the 1990s. Only three Seawolves were built. The Seawolf was designed for the Cold War, carrying 50 weapons (torpedoes, cruise missiles, or Harpoon anti-ship missiles) for its 8 660 mm (26-inch) torpedo tubes. Seawolf was fast (top speed of over 60 kilometers an hour) and much quieter than the Los Angeles boats. the Virginia-class was designed to replace the cancelled Seawolves. Think of the Virginias as Los Angeles size hulls with a lot of Seawolf technology installed. The Virginia class boats ended up costing about half as much as a Seawolf. But that was largely possible because the Virginias used a lot of the new technology developed for Seawolf.

 


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