The ASW Mission Package — part of the interchangeable sets of technologies being designed for both the USS Freedom and USS Independence variants of the LCS — is being engineered such that it can detect submarines with a Multi-Function Towed Array (MFTA) and what’s called Variable Depth Sonar (VDS), said Capt. John Ailes, LCS Mission Modules program manager.
“Variable Depth Sonar allows us to put the sound down where the submarine is. If you look on current destroyers, they have a hull-mounted sonar on the bow. It turns out that there are acoustic layers based on temperature and pressure that bend the sound up. A submarine can dive below this layer and there is a lot of attenuation and signal loss from a hull-mounted sonar,” Ailes explained.
The Variable Depth Sonar allows sailors to place the sonar “beneath this layer,” Ailes said.
MFTA is a towed array sonar system, tethered to the ship, that is able to receive and transmit signals, including sounds and signals emerging from the VDS, Ailes explained.
The MFTA, called the AN/TB-37, is currently fielded on 30 US Navy cruisers and destroyers, said Navy spokesman Matt Leonard.
“The VDS variable depth sonar is an active sound producing system that provides the acoustic signal that is sent out and reflected back from the target submarine. The reflected sound is received on the MFTA. The VDS and the MFTA are towed separately but they can be towed at the same depth, or at different depths. Generally they are towed independently at the same depth,” Leonard said in written statement.
The combination of these two detection systems will allow the LCS to better detect quiet submarines such as diesel subs running only on batteries, Ailes added.
“Together, the VDS and MFTA provide both a transit speed ASW escort, and a barrier/area search capability, as well as a torpedo alert capability,” Leonard said.
Don’t mistake the capabilities of the VDS with the hull mounted SQS-53C sonar on cruisers and destroyers. The VDS can be towed at depth.
“Cruisers and destroyers can tow their MFTA’s at depth, but if the submarine is deep, they can only receive the sound the sub makes. In comparison, the VDS is effective against quiet submarines as it produces the sound which is then received on the MFTA,” Leonard added.
The Navy is currently testing with a VDS that is made by Thales, Leonard indicated.
“This system has been in service since 2004, but this is the first time it has been used by the U.S. Navy. We will be having a competition for the Mission Package’s production VDS and it is likely that Thales will be one of the offerers,” Leonard added.
Overall, the Navy plans to acquire as many as 16 Anti-Submarine Warfare Mission Packages to serve on portions of the planned-for 55 LCS ships.
The ASW mission package is also configured to work in tandem with UAS such as the Fire Scout and airborne torpedoes on-board the Navy’s MH-60R helicopter.
The MH-60R can also lower active and passive sonar sensors using a sonobouy device; in fact, the MH-60R can make use of a dipping Variable Depth Sonar which drops into deep water from the air, Ailes added.
In addition, the ASW Mission Package is equipped with a defensive technology called Light-Weight Tow that is able to defeat incoming enemy torpedoes, Ailes explained.
“It defeats a torpedo when it is shot at the ship. If there is an torpedo inbound, it defeats it and there is no operator action required,” said Ailes.