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SSN-637 Sturgeon class

STURGEON class submarines were built for anti-submarine warfare in the late 1960s and 1970s. Using the same propulsion system as their smaller predecessors of the SSN-585 Skipjack and SSN-594 Permit classes, the larger Sturgeons sacrificed speed for greater combat capabilities. They are equipped to carry the HARPOON missile, the TOMAHAWK cruise missile,and the MK-48 and ADCAP torpedoes. Torpedo tubes are located amidships to accomodate the bow-mounted sonar. The sail-mounted dive planes rotate to a vertical position for breaking through the ice when surfacing in Arctic regions.

In the early 1960s the submarine community emphasized continued improvements in quieting, both array and processing gain, better sonar system integration, and formal tactical and operational analysis. Beginning with the Thresher/Permits, American SSN designs demonstrated a continuing willingness to emphasize quieting over other valuable operational capabilities such as speed and diving performance. Thus in the progression from Skipjack to Thresher to the Sturgeon class in 1967, there were significant improvements in quieting with each generation, and a loss in several knots of top speed.

USS Sturgeon (SSN 637) was originally conceived as a modest upgrade to the Permits but she grew to become a class of her own. She was larger, both because quieting and size tend to accompany each other, and because she was given more space to accommodate a more advanced acoustic and SIGINT sensor suite. With the 637s the submarine force began to embrace LOFAR (LOw Frequency Analysis and Ranging) signal processing as a tool for both detection and classification. LOFAR provided an additional, very powerful tool for increasing acoustic signal-to-noise ratios. Using LOFAR, the sonar focuses only on those low frequency tonals where the submarine's source levels are highest. The sonar can therefore detect that narrow component of the submarine's overall sound spectrum at much greater ranges before noise drowns it out.

Experimental spectrum analyzers like the BQQ-3 were replaced in the early 1970s by digital systems and were deployed on all submarines rather than only those engaged in special missions. The 637s were also the vehicle for early experiments with towed arrays. Towed arrays were line arrays of omnidirectional hydrophones much like SOSUS arrays that used electronic beamformers to achieve array gain. Long, thin, towed arrays could provide more aperture than could bow or hull-mounted arrays, and also suffered less from self noise and flow noise.

One of the first and most important uses for both LOFAR and the towed array in the submarine force was the creation and maintenance of a library of Soviet submarine signatures. Each class of submarine, and indeed each submarine, generated its own unique blend of narrow and broadband sound at varying levels. Knowledge of these signatures was fundamental to the effective use of LOFAR, and to predicting the performance of passive sonars. Even the most advanced computers of the day were limited in the number of spectral lines that they could process, meaning that prior knowledge of the frequency of those lines was necessary in order to maximize LOFAR capabilities. Likewise, predicting the performance of passive sonars demanded knowledge of the strength of the target signal. Knowledge of sonar performance was fundamental to the barrier strategy because expected detection range was the key variable in determining the number of platforms needed to man a given barrier. Submarines were uniquely able to collect and maintain this data base of opposing submarine signatures, which served both their own operations as well as the other ASW communities.

Another unique capability provided for the first time on a large scale by the 637s was an enhanced ability to covertly track an opponent. Prior SSNs could certainly track their Soviet counterparts, but the tactical challenges involved were significant. Tracking operations demanded the ability to approach the target covertly and establish and maintain a position to its rear, in its so-called "sound baffles." The situational awareness required to do this was demanding, because the distance from which the track was maintained was at relatively short, direct path ranges where counter detection was most likely. Alongside the fact that it was quiet, a 637's large, spherical, bow sonar array gave its crew a wider angle view in both azimuth and elevation of its target than did a Skipjack or a Skate. This effectively removed a set of blinders which constrained the field of regard to a narrow cone looking forward. The 637s made it feasible to develop tactics for routine, covert tracking operations that could be implemented on a force-wide basis.

USS Sturgeon (SSN-637), the lead ship of a 37-unit class, was commissioned in 1967. This class introduced General Dynamics to submarine construction. That same year New York Shipbuilding Corporation dropped out of submarine construction while building USS Pogy (SSN-647); she was towed to Ingalls Shipbuilding in Pascagoula, Mississippi to be completed. Portsmouth Naval Shipyard dropped out of the nuclear powered submarine construction business in 1971, and Mare Island Naval Shipyard dropped out of the nuclear powered submarine construction business the following year. Ingalls Shipyard dropped out of the nuclear powered submarine construction business in 1974. This action left only General Dynamics Electric Boat and Newport News Shipbuilding as the U. S. Navy's only source of new construction nuclear powered submarines.

Beginning with SSN-678 Archerfish units of this class had a 10-foot longer hull, giving them more living and working space than previous submarines of the Sturgeon Class.

A total of six Sturgeon-class boats were modified to carry the SEAL Dry Deck Shelter [DDS], one in 1982 and five between 1988 and 1991. The are SSN 678-680, 682, 684, 686 are listed as "DDS Capable" -- either permanently fitted with the DDS or trained with them. In this configuration they are primarily tasked with the covert insertion of special forces troops from an attached Dry Deck Shelter (DDS). The Dry Deck Shelter is a submersible launch hanger with a hyperbolic chamber that attaches to the ship's Weapon Shipping Hatch. The DDS provides the most tactically practical means of SEAL delivery due to its size, capabilities, and location on the ship.

Rapidly phased out in favor of the LOS ANGELES and SEAWOLF Classes of attack submarines, this venerable and flexible workhorse of the submarine attack fleet continues to operate in the forward areas of the world to this day. Attracting little publicity during its heyday, this class of ship was the platform of choice for many of the Cold War missions for which submarines are now famous. After a 5-year study was completed on the SSN-637 class submarine, the design life was extended from 20 years to 30 years, with a possible extension to 33 years on a case-by-case basis. However, many boats of this class were retired prior to this limit in order to avoid expensive reactor refueling operations.

While almost all Cold War operations remain classified, recently declassified missions showcase Submarine Force capabilities. In 1978, in the Atlantic, USS Batfish (SSN-681) tracked a Soviet ballistic missile submarine (SSBN) sailing off the East Coast of the U.S.- learning Soviet SSBN patrol areas and operating patterns and providing early indications of any potential surprise attack on the U.S.



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