SAN DIEGO – U.S. Navy undersea warfare experts are asking Applied Physical Sciences Corp. in Groton, Conn., to develop an undersea sensor and emitter system able to disrupt or defeat sonar systems aboard hostile surface warships under terms of a $12.5 million order announced last week.
Officials of the Naval Information Warfare Center Pacific in San Diego are asking Applied Physical Sciences to begin the second phase of the Willow program to develop innovative payloads to conduct acoustic warfare to counter active surface sonars.
Applied Physical Sciences joins Systems & Technology Research (STR) LLC in Woburn, Mass., on Willow phase two. STR won a $9.6 million order for this project in late January. The Naval Information Warfare Center Pacific awarded the Willow orders on behalf of the U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va.
Applied Physical Sciences and STR engineers will place these counter-sonar payloads on uncrewed underwater vehicles (UUVs), buoys, moored systems, and other nodes for validation and at-sea demonstrations. The Willow program's second phase will involve a sea test to demonstrate three or more nodes to counter enemy surface active sonar systems.
Ship-mounted sensors
Surface sonar is a ship-mounted underwater acoustic sensing system used to detect, track, and classify submarines, torpedoes, mines, and underwater obstacles. It works by transmitting sound pulses into the water and listening for reflected sounds. It's typically aboard surface ships like destroyers, frigates, and corvettes.
Willow's first phase involved at-sea tests to demonstrate counter-sonar capabilities from one node. Applied Physical Sciences and STR both were participants in Willow phase one, for which contracts were awarded in 2023.
The project includes independent verification and validation, hardware-in-the-loop simulations, and at-sea testing. These most recent orders bring the Applied Physical Sciences contract's value to $27.8 million, and STR's Willow contract to $20.5 million.
Acoustic warfare involves deceiving and spoofing enemy surface sonar systems designed to detect and track submerged submarines. It seeks to counter active surface sonars with enabling technologies to degrade, deceive, or complicate the effectiveness of active surface sonar.
Active sonar
Active sonar works by transmitting an acoustic pulse, or ping, and analyzing acoustic echoes. Countermeasures focus on reducing echo quality, introducing false echoes, or overwhelming signal processing. It typically involves UUV-mounted, towed, or expendable acoustic decoys that emit or reflect sound to mimic a submarine or other target.
Acoustic warfare also can involve broadband noise jamming that raises background noise to reduce signal-to-noise ratio; deceptive jamming that retransmits modified versions of the incoming ping to create range, bearing, or speed ambiguities; acoustic absorption and signature reduction; use of thermoclines, salinity layers, and bottom clutter to scatter or refract sound; echo enhancement and clutter generation; and sonar warning receivers that detect active pings to enable timely maneuvering or countermeasures releases.
Modern active sonars can employ adaptive waveforms, multistatic operations, and advanced signal processing to reduce the effectiveness of simple noise jamming. Countermeasures increasingly emphasize deception and signature management over brute-force noise.
Sonar spoofing
Willow seeks to develop revolutionary advances in payloads, hardware, and signal processing that can confound or defeat active sonar detection by using advanced acoustic hardware and waveforms, as well as new digital signal processing techniques.
On this order, Applied Physical Sciences will do the work in Orange, Calif; Groton and Pawcatuck, Conn; Arlington and Reston, Va.; and Concord, Mass., and should be finished by February 2027. STR, meanwhile, will do its work in Braintree, Springfield, and Woburn, Mass.; South Kingstown, R.I.; and Arlington, Va., and should be finished by January 2027.
For more information contact Applied Physical Sciences online at https://aphysci.com/sensing-systems/, Systems & Technology Research online at https://str.us/technology-platform, or DARPA at www.darpa.mil.
