Submarines: Rapidly Evolving SSNs

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January 19, 2019: The U.S. Navy unexpectedly revealed in 2018 that it was returning the ENCAP (encapsulated in a container that is fired from a torpedo tube) Harpoon anti-ship missile to active service. The Navy withdrew the ENCAP Harpoon in 1997 but in 2018 test fired one of them (apparently refurbished for the occasion) and found they still worked as they were supposed to. The ENCAP Harpoons were initially replaced by an anti-ship version of the Tomahawk, which was also soon withdrawn. With the collapse of the Soviet Union in 1991, the major naval adversary of the United States soon disappeared. The smaller Russian state could not afford to maintain, much less operate, much of the huge Soviet fleet.

By American 1999 subs were just carrying land attack Tomahawks, not just because the Soviet navy was gone but also because for either Harpoon or Tomahawk you have to have a general idea of where the target is before you fire the missile, which has its own terminal guidance system for locating a ship nearby and hitting it. But the subs rely on stealth for protection and that means few transmissions while underwater. For the ENCAP Harpoon, the 1990s passive sonar could locate a surface target out to about a hundred kilometers (under the right conditions). Half that was needed, (in most cases) for the Mk48 torpedo, which also a terminal guidance system and could, at slow speed, reach a target out to about a hundred kilometers.

In any event, a lot has changed since the 1990s when it comes to passive (just listening) sonar the subs use most of the time, as well as the tech used for a submerged sub to receive (or send, when necessary) electronic information. Subs now have many more “periscope” capabilities. The conventional optical periscope has been replaced by devices that can be sent to the surface tethered by cable. These tethered devices can receive satellite and other electronic messages, as well as send. That means a sub could be ordered to send up the sat receiver so many times a day when in a combat zone to receive updates on enemy activity. These could include firing orders for distant ships (or land targets) to be fired on using missiles. The latest version (Block II+ER) Harpoon has a 300 kilometer range and much better terminal guidance and countermeasures. But it is still a slow (800 kilometers an hour) missile while the most modern anti-ship missiles have terminal attack speeds of more than three times that. Then again for a surprise attack Harpoon can be useful as it comes in very (“sea skimming”) low often avoiding enemy radar. So a possible situation would have an enemy ship detected by satellite or UAV with location information sent to a sub within Harpoon range (or able to move into range) which could then fire one or more ENCAP Harpoons and then go hide. ENCAP Harpoons blasting from the sea surface makes a lot of acoustic and visual noise. Another option is the ENCAP UAVs proposed for subs. These can be launched more quietly and spend several hours searching an area for any targets and sending the sub brief message bursts with the location of any targets.

The navy is not spending a lot of money on bringing the ENCAP Harpoon back into service. It is going to upgrade some older Harpoons and ship then as ENCAP weapons for possible use under the right conditions. The navy, as expected, isn’t providing details and the details may involve some new tech or tactics that are best kept secret.

What the Navy is spending a lot of money on is new subs. The Navy is putting its 17th Virginia class SSN (nuclear attack sub) into service in February. The South Dakota (SSN 790) took three years to build and is the seventh of eight Block 3 Virginias. Ten years ago the navy got its fifth Virginia eight months ahead of schedule and under budget. At that point, the Virginia’s were taking 5-6 years to build and are arriving at the rate of one a year. Over the last five years, the speed of construction has increased as well as the rate of delivery (now one or two a year) in order to replace the aging Los Angeles class boats. In one recent 25 month period five Virginias were put into service.

Each block of Virginians represents improvements, some of them substantial. There are (or will be) four Block 1s, eight Block 2s, eight Block 3s, ten Block 4s and ten Block 5s. The Navy now plans to build 66 Virginias with ten currently under construction and 17 in service (or undergoing sea trials). Blocks 1-4 of Virginia are all armed the same way but Block 5 (arriving in the early 2020s) will have additional space to store and launch missiles and will carry 65 missiles and torpedoes (75 percent more than Block 1-4 boats). This will be accomplished by adding an additional section (the VPM or Virginia Payload Module) that adds 25.6 meters to the length of the sub and increases displacement to 10,400 tons. Each new Block gets better electronics and sensors and it is believed that the passive sonar in the late model Virginias have much longer and accurate detection ranges. The Block 5 will also receive a large number of equipment upgrades.

The Block 1-4 Virginias cost about $2.2 billion each. They displace 7,800 tons and are 114.9 meters (377 feet) long and 10.36 meters (34 feet) wide. Top speed is over 50 kilometers an hour, max depth is more than 250 meters (over 800 feet). The Block 1-4 Virginias 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 naval mines.

More important are the large number of electronic systems carried. These make the Virginias more difficult to detect, 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) outside 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 2 models used less costly construction techniques, while the eight Block 3 boats have some design changes and new technology. The most dramatic improvements will come with Block 5.

The U.S. currently has three classes of SSN. Most are the 6,900 ton Los Angeles-class SSNs. Sixty-two of these submarines were built and 32 are still in service. Armed with four 53.3 cm torpedo tubes, they carry twenty-six weapons for those tubes (either the Mk 48 torpedoes or BGM-109 Tomahawk cruise missiles). The last 31 Los Angeles-class SSNs 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. But there’s barely enough money to keep building Virginias and no time or cash to refurb elderly Los Angeles class boats. That was why the number of Virginias planned was increased to 66 and the tempo of construction speeded up. Thus the American SSN fleet will not shrink from 55 in 2013 to under 45 by 2030. The current building plan keeps the SSN numbers at or above fifty.

Twenty-nine 9,000 ton Seawolf-class SSNs were supposed to replace the Los Angeles boats but Seawolf proved too expensive. Only three were built. The Seawolf was designed for the Cold War, carrying fifty weapons (torpedoes, cruise missiles, or Harpoon anti-ship missiles) for its eight 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. To replace the un-built Seawolfs the Virginia-class was designed. Think of it as a Los Angeles size hull with a lot of Seawolf technology installed. The Virginia class boats ended up costing about half as much as the Seawolfs. But that was largely possible because the Virginias used a lot of the new technology developed for Seawolf.

 


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