Defenses against swimmer incursions are security methods developed to protect watercraft, ports and installations, and other sensitive resources in or near vulnerable waterways from potential threats
Maritime law enforcement specialists at Regional Dive Locker East in Portsmouth, Va., prepare for a training dive
"OWL"-type surface ROV (also known as the Unmanned Harbor Security Vehicle) used to search for submerged divers
Sonar
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Sonar is a technique that uses sound propagation to navigate, measure distances, communicate with or detect objects on or under the surface of the water, such as other vessels.
Defense against swimmer incursions
…but did bring renewed attention to the vulnerability they present for naval ships. Divers can swim 100 to 200 yards in about three minutes, and large sonar ranges would be required around ships for security forces to detect underwater swimmers in time to make an effective response. In March 2005 the…
French F70 type frigates (here, La Motte-Picquet) are fitted with variable depth sonar (VDS) type DUBV43 or DUBV43C towed sonars.
A sonar image of the Soviet Navy minesweeper T-297, formerly the Latvian Virsaitis, which was shipwrecked in December 1941 in the Gulf of Finland.
Fessenden operating underwater oscillator in 1915.
Bubble clouds shown under the sea. From ref.