ARLINGTON, Va. – U.S. military researchers needed new undersea sensor and emitter systems to disrupt or defeat adversary surface sonar systems. They found a solution from Systems & Technology Research (STR) LLC in Woburn, Mass.
Officials of the U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va., announced a $9.6 million order to STR in late January for the second phase of the Willow program to develop acoustic warfare systems to counter enemy active surface sonar systems.
STR undersea warfare experts 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 programs second phase will involve a sea test where to demonstrate three or more nodes to counter enemy surface active sonar systems.
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 for destroyers, frigates, and corvettes.
Countering surface sonars
Willow's first phase involved at-sea tests to demonstrate counter-sonar capabilities from one node. Also participating in Willow phase-one was General Dynamics Applied Physical Sciences Corp. in Groton, Conn. Willow phase-one contracts were awarded in 2023.
The project includes independent verification and validation, hardware-in-the-loop simulations, and at-sea testing. This order brings the cumulative face value of the 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 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.
Advanced signal processing
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.
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, STR will do the 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 Systems & Technology Research online at https://str.us/technology-platform, or DARPA at www.darpa.mil.
