Not content with firing more than 1,000 rockets and missiles at Israel in recent days, Hamas has twice dispatched “frogman terrorists” to try to attack Israel. The attempts were foiled, but they brought out the fact that with hundreds of kilometers of shoreline to patrol, catching maritime infiltrators is a major challenge for Israel.

It’s difficult enough to find invaders on land, where cameras, sensors, and perimeter detection systems provide security personnel with effective tools to detect terrorists, but for invaders from the sea, those solutions are largely ineffective. An answer might come from Israeli defense technology firm DSIT Solutions, which offers various configurations of below-water sonar and electronic detectors designed to protect bays, harbors, and ocean-based installations (like oil rigs), piers, ports, and energy terminals.

DSIT technology is deployed off the Israeli coast, the Israeli Navy and DSIT said. Neither would say, however, if the recent attempts by Gaza frogmen terrorists were foiled by the company’s technology. The firm, located in the Tel Aviv suburb of Givat Shmuel, has been part of a US holding company called Acorn Energy since 2009.

Sonar (originally an acronym for SOund Navigation And Ranging), involves using sound propagation to detect objects underwater. Sound is the best way to detect movement underwater, because sound waves travel farther in the water than do radar and light waves, scientists say. DSIT systems use both active sonar transducers, which emit an acoustic signal or pulse of sound into the water that bounces off the object and returns an “echo,” as well as passive sonar systems, which listen for sounds. In both systems, the strength of the sound indicates the distance and size of the object.

To catch frogmen and other undesirables, DSIT deploys its AquaShield Diver Detection Sonar (DDS), which, the company says, can detect over 1,000 targets simultaneously from several kilometers away. What makes sonar effective as a security tool is the analysis software behind it, which needs to differentiate between real threats and other objects in the water, like fish. The AquaShield, DSIT says, has advanced algorithms that can tell the difference between “normal” underwater objects and others.

The dangers from the sea go beyond frogmen. Also on the watch list of security personnel are Swimmer Delivery Vehicles (SDV) and Diver Propulsion Vehicles (DPV), underwater “pods” and scooters that can quickly move divers from a ship far out at sea closer to the coast. These vehicles can also carry equipment. Sophisticated SDVs may even contain detection systems to alert divers to the presence of security or naval units, so that they can lie low until the coast is literally clear, making the task of catching them all the more difficult. Unmanned Underwater Vehicles (UUV), an additional threat, are underwater drones that can be equipped with bombs, set to blow up in a harbor or port.

To counter these threats, DSIT offers its AquaShield ER, specifically designed to detect fast-moving SDVs and UUVs. Before its introduction, DSIT put the system through its paces, achieving detection ranges of up to 3,500 meters for SDVs.

Among DSIT’s customers are numerous navies around the world, including the Israeli Navy. According to Commander R. Leshem, head of the Navy’s anti-submarine warfare branch, Israel has been using DSIT technology “for quite some time now. We operate these systems around the clock to protect critical coastal sites and marine assets. We have found that these systems are reliable, easy to work with, and provide a good answer to our operational requirements. I definitely would not like to be a combat diver on an attack mission facing one of these underwater surveillance systems.”

DSIT CEO Benny Sela said, “We greatly value our good working relations with the Israeli Navy, which has been an important source of feedback regarding their operation of our systems, and are proud to be a vital element in their advanced security framework. DSIT is continuing to enhance its systems based on feedback from all of our customers.”