Defense against swimmer incursions

The need for military underwater security was demonstrated in World War II by the achievements of frogmen against armed forces facilities such as the Italian frogman actions in WWII.

Since the late 1950s, the increasing demand for and availability of sophisticated scuba diving equipment has also created concerns about protecting valuable underwater archaeology sites and shellfish fishing stocks.

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.

[2][clarification needed] Zones of operations include: Potential theaters of operation:[citation needed] Maintaining underwater security against intrusion on or under the water has been complicated by the expansion of recreational scuba diving since the mid-1950s, making it unacceptable in most democracies to use potentially lethal methods against any suspicious underwater sighting or sonar echo in areas not officially closed to recreational divers.

One result was an incident in the inter-ethnic crisis in Cyprus in 1974 when a tourist was arrested for suspected spying because "frogman's kit" was found in his car; it was ordinary sport scuba gear.

[citation needed] Another result of sport diving is a risk of civilians independently re-developing, and then using or selling on the free market, technologies, such as technical advances in underwater communications equipment, formerly kept as military secrets.

[citation needed] There have been incidents which have demonstrated poor underwater security, such as when a sport diver with a noisy, bubbly, open-circuit scuba and no combat training entered a naval anchorage and signed his name on the bottom of a warship.

[2] Analysis of research literature related to effects of ultrasound concluded that reported ultrasound-caused organ damage was associated with sound pressure levels exceeding a certain intensity threshold, regardless of frequency[2] The UPSS/IAS diver-detector sonar system includes an underwater shockwave emitter.

[8] The sea lion is trained to detect the diver, connect a marker buoy to his leg by a C-shaped handcuff-like clamp, surface, and then bark loudly to raise the alarm.

[citation needed] From 1970 to 1980 trained dolphins killed two Soviet frogmen who were putting limpet mines on a US cargo ship in Cam Ranh bay in Vietnam.