The U.S. Navy's new towed sonar has survived lawsuits and budget cuts to become a major tool in dealing with increasingly dangerous non-nuclear submarines lurking in coastal waters. The SURTASS LFA (Low-Frequency Active) system (WQT-2) has emerged from a court battle with a legal settlement that allows limited training. The new active sonar adjunct to the passive UQQ-2 will be deployed on a transducer lowered to a depth of 330 feet, with the vessel sailing at 5.55 kilometers per hour, operating on a 10 percent duty cycle (which is about how long the sonar will be transmitting active pulses). The WQT-2 is an upgrade to the existing SURTASS system, which is a passive system (in the case of the UQQ-2, a lot of microphones placed on a 1,830-meter cable). For shallow water, a twin-line towed array, using two shorter arrays, is used. The ships currently using the passive system have also received the SURTASS Block Upgrade, which includes a reduced diameter array and SATCOM UHF so that ocean surveillance ships can communicate better with tactical vessels (like the Oliver Hazard Perry-class frigates and the Arleigh Burke-class destroyers).
SURTASS LFA will be used to detect advanced non-nuclear submarines in shallow waters along coasts, particularly the new classes of subs that are using fuel cells. The new submarine classes (the Russian Amur and Lada classes, the French Scorpene, and the German Type 214) use fuel cells instead of diesel engines to charge their batteries. Diesel engines, while reliable, are noisy, and making noise is a good way to attract the not-so-friendly attention of opposing naval forces. The fuel cells and air-independent propulsion systems are much quieter, and, most importantly, enable the sub to stay underwater for days at a time. This allows them to get closer to potential targets (most likely carriers and amphibious vessels) before they are detected.
In anti-submarine warfare, particularly against submarines, detection range is important. The newer, quieter subs have the potential to get close enough to launch anti-ship missiles like the C-802 (with a range of 120 kilometers), Harpoon (140 kilometers), Yakhont (120 kilometers), or Exocet (the missile made famous in the Falklands, with a range of 65 kilometers) before they are detected. Those missiles could ruin any surface ships day. Particularly when those ships have to enter littoral waters.
The WQT-2 is intended to increase the detection range, particularly in shallow waters near the coastline, and to thus regain the reaction time that passive systems can no longer provide reliably. The increased reaction time could be used to evade the submarine, forcing it to either attack from an unfavorable position, or to speed up to get into a good attack position, and thus make noise. The latter would make the submarine easier to detect. Once a hostile submarine is detected, it would be dealt with. One method would be to vector in P-3 anti-submarine aircraft to deliver torpedoes like the Mk 50 Barracuda and Mark 54 Lightweight Hybrid Torpedo (LHT), killing the sub before it can launch an attack. Another would be to allow a friendly submarine (probably nuclear-powered) to deal with it.
The system prototype is deployed on a leased vessel, the R/V Cory Chouest, and is slated to deploy on the USNS Impeccable (T-AGOS 23) in 2004. Plans exist for as many as four to be deployed down the road, two in the Atlantic, two in the Pacific (probably the Victorious-class ocean surveillance ships) once a compact version is developed. Harold C. Hutchison
