Anti-frogman techniques are security methods developed to protect watercraft, ports and installations, and other sensitive resources both in or nearby vulnerable waterways from potential threats or intrusions by frogmen or other divers.
In World War II this need for military underwater security was first shown by the achievements of frogmen against armed forces facilities: see for example 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.
The 12 October 2000 USS Cole bombing was not carried out by underwater divers, but did bring renewed attention to the vulnerability they present for naval ships. Divers can swim 100 to 200 yards in three minutes time, and large sonar ranges would need to be established around ships in order for security forces to detect underwater swimmers in time to make a sufficient response.
In March 2005 the Philippine military, interrogating a captured anti-government terrorist bomber, found that two of Southeast Asia’s most dangerous terrorist organizations linked to Al Qaeda were said to be jointly training militants in scuba diving for attacks at sea.
Following World War II, the increasing popularity in recreational diving introduced a new complexity to underwater security. Divers must not only be detected, but evaluated as to their purpose or intentions for swimming in monitored areas. Steps to protect against threat or harm from divers must take into account possible reasons why they would be swimming in monitored areas. The divers may be:
Swimmers can approach from the surface or underneath the waters, the two presenting their own detection and deterrence challenges. And the interception and apprehension of intruders detected in bodies of water pose unique safety risks.
There are various types of places of operation:
There are these likely theaters of operation:
A police-type technique that is reasonably safe on land may be risky to a scuba diver.
Keeping underwater security against frogman intrusion has been complicated by the expansion of sport diving since the mid-1950s, making it bad policy for most democracies to use potentially lethal methods against any suspicious underwater sighting or sonar echo in areas not officially closed to sport divers. Any routine patrol investigation of all "unidentified frogman" reports would have had to stop because any genuine reports of intruders would be swamped in ever more reports of civilian sport divers who were not in military areas.
For a long time it would be easy for diving professionals and other experienced divers to distinguish a sport diver with an open-circuit scuba such as an aqualung from a combat frogman with a rebreather; and legitimate civilian divers are normally fairly easy to detect because they dive from land or from a surface boat, rarely or never from an underwater craft, and willingly advertise their presence for their own safety; but recent multiplication in sport rebreather use may have changed that somewhat.
In the past, when scuba diving was less common, many non-divers, including police, patrol and guards, knew little about diving and did not know of this difference in diving gear, but described all divers as "frogmen". 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.
After about 1990 the rapid growth in the number of sport diving rebreather brands has clouded this distinction, while advanced sport divers increasingly tackle longer, deeper, riskier dives using equipment once available only to armed forces or professionals. This means that even "less-lethal" techniques for trapping them underwater, disorienting them, or (especially) forcing them to the surface would be an ever-increasing risk to civilian divers' lives.
In former times, civilian diving was only for work, and needed standard diving dress and large, readily visible surface support craft. Sport scuba diving has changed that.
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. (For a loss of military secrecy caused by independent civilian duplication, though not underwater, see Lokata Company.)
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. Concern at the risk of increasing the sport-diving public's ability to penetrate harbors undetected, and of unofficial groups equipping combat frogmen from the sport scuba trade, might have led to the events listed at "#Prevention" below.
Examples of diver-detecting active sonar systems are:
These links    claim that after 9/11 the FBI asked the USA's largest scuba diver certification organizations to turn over the records of all divers certified since 1998; this turning-over is now done once a year.
Some anti-frogman weapons, and weapons that may come to mind when considering defending against frogmen, are:
This is the usual method available to non-diving harbor guards, and to unofficial groups trying to restrict or prevent scuba diving in their area. For weapons, see the next section.
In some circumstances, submerged open-circuit scuba divers can be followed by their bubbles until they run out of air and have to surface, and then tackled on the water surface or as they come ashore.
According to circumstances, the patrol may need some means of transporting prisoners and/or seized diving equipment away from site.
Many casual sport diving intruders may keep away on seeing visible clearly marked patrol boats and surface barriers.
These methods may be useful when assault-boarding a boat being used by unauthorized or suspect divers, or arresting them onshore, but not often otherwise.
Ordinary bullet-firing firearms may be useful (as a lethal weapon) against divers on the surface or men in boats or ashore, but underwater are inaccurate and very short range.
A depth charge is effective, and may be lethal, but may cause other damage underwater, and is not recommended in peacetime when the victim may be an intruding civilian sport diver, although it is alleged to have been common practice for some years after 1945 in British naval harbors.
Divers, however, are far less vulnerable to damage by underwater explosion than common sense would dictate. Since the tissues of the body tend to transmit the shock waves with much the same characteristics as the water around, large distant shocks have little impact on divers. For this reason, the most effective "depth charge" for use against a diver is the common hand-grenade, tossed within a few feet of the diver. The resulting gas cavitation and shock-front-differential over the width of the body is effective in stunning or killing the diver.
A magnetic field generator to make the diver's navigation compass misread is possible. Such a magnetic coil carried by a patrol boat directly over the target diver would affect compass readings to 5 meters (15 feet) depth at about 7 kilowatts; but to 10 m (30 feet) (oxygen rebreather depth limit) at about 448 kilowatts, which is too much power need to be practical.
Requirements are different according to what sort of weapon is called for:
There has been much research about the effect of sound on divers.:51 et seq.
High intensity sound 20–100 Hz, and high intensity impulse noise, are promising as a non-lethal weapon, but more testing is needed.:47 As a source of high-intensity 20–100 Hz sound, the sound generated by a plasma sound source is promising.:42–43
The US Navy Diving Manual  says that high-power low-frequency sonar (commonly used for depth sounding and to detect large objects (including submarines)) is not good at detecting small objects like divers, but is hazardous to divers.:3
As each wave of the ultrasound passes through the diver, any bubbles in the tissue expand and contract, and the tissue heats. After a particular threshold of loudness of the ultrasound, new bubbles form during the low-pressure part and disappear during the high-pressure part: this is cavitation and can cause injury.
One method is a powerful blast from a ship's ordinary high-power low-frequency sonar (commonly used for depth sounding and to detect large objects (including submarines)), which deranges the diver's inner ear and makes him dizzy and disoriented and tends to force him to surface, or may make him panic and lose his mouthpiece and drown. These large "active sonars" are used to search for submarines and are very powerful. These sonars are usually bow mounted, and if so a diver attacking at the stern would be in the sonar baffle region and unaffected, if he gets close enough first.
Most ships, both military and non-military, carry smaller "navigation" sonars such as depth finders or collision sensors, but their high frequencies and relatively low power lack effectiveness against divers.
Some say that these speculations are mostly fanciful and that since the human body is very close to the impedance of the water around it, the ultrasound tends to pass through the body (perhaps breaking the eardrum, but not killing the diver); but if the sound or ultrasound is powerful it may cause overheating or cavitation damage on the way.
It is unknown what later proof or disproof there has been of speculations such as appeared in a book about Cousteau written by Philippe Diole around 1960, about underwater ultrasound guns making an ultrasound beam powerful enough to disintegrate a diver into the water except the metal parts of his kit.
A sound that irritates or causes pain.:27–28 Diver aversion to low frequency sound is dependent upon sound pressure level and center frequency. Westminster International have also implemented this but they withhold the exact sound frequencies used.
The sound may be an order to surrender or surface or go onshore or to the patrol boat, perhaps with a threat to use non-lethal or lethal force if disobeyed. But such an order must be clear enough to be heard and understood.
Underwater, human hearing is largely by bone conduction, through the skull and not through the eardrum and ossicles. This causes somewhat less acuity of hearing and a different graph of sensitivity against frequency, with a loss between 1000 Hz and 5000 Hz. This may affect ability to understand speech.
Research showed that, at depths up to at least 10 m (30 feet), divers' wetsuit hoods lessened underwater hearing sensitivity by 10 to 35 decibels at 1000 Hz and above, and by little or nothing at 250 Hz and below. With increasing depth in a hyperbaric chamber, decreases in wetsuit hood sound attenuation appear only to occur at frequencies between 500 and 1500 Hz. In the open ocean, hood attenuation at 8,000 Hz showed a significant decrease at 60 fsw and a tendency to decrease at 2,000 and 4,000 Hz compared with the 10 fsw data at the same frequencies in the chamber trials. At frequencies from 500 to 4,000 Hz wetsuit hood sound attenuation was on average 8 dB lower in the ocean than in the chamber trials.
A newspaper article about the Lionel Crabb disappearance speculated about underwater electric shock weapons mounted on warships to defend them from frogmen. This method, if it is used, imitates nature; see electric eel and electric ray.
Small dredging-type craft and small submarines are used for small-scale dredging and/or to recover submerged objects; but there is no known case in the real world of them being used to capture divers. The craft's capture device might be a net or a grab or an aimable suction tube or a scoop.
An article at the American Academy of Underwater Sciences 1991 International Symposium Proceedings says that the California Department of Fish and Game, to capture sea otters underwater for a relocation program, successfully used a net cage apparatus front-mounted on a Dacor Scooter diver propulsion vehicle steered by a diver with a silent bubbleless closed circuit oxygen rebreather. It is not known if a similar larger device has ever been used to capture divers underwater.
A suction device might make an area suction effect in the open, or might be a suction tube extended at the frogman, who may be sucked against an opening and so held, or may be sucked inside.:36.7
Such devices on a small scale are sometimes used in nature to catch prey: for example by the seahorse and the pipefish, and the bladderwort plant. The mouths of many teleost fish (for example centrarchids) have a strong suction component to the way they work.
Barriers can be put in the water to exclude swimmers and frogmen.
There is concern that these nets could interfere with fish migration. Due to this and expense one opinion says that they are a poor choice as frogman excluders.:14 et seq.
This is metal chain-link netting placed underwater, preventing entry into an area, or at least delaying the frogmen while they cut through it.
It was made by an Israeli company, RBtec Perimeter Security Systems. It is a netting constructed of copper or fiber optic cable, covered in polyethylene electrical insulation. The strands are a sensor cable sensitive to cutting or shape bending so that any frogman attack on the net will be detected. The grid size best suited to deter divers is 250 x 250 mm = 10 x 10 inches but can be modified to any size needed. Testing showed that a diver using bolt cutters could not cut a hole big enough to swim through without being detected. In order to prevent attempts of crossing above or under the net the company utilize multiple sensors to detected lifting or climbing of the net. The net can also be integrated with sonars and floating barriers for a more complete security solution.
The net system can be equipped with a gate, to allow traffic in and out of the protected area.
These will stop surface boats from dropping divers in restricted areas.:14 et seq.
One effective anti-swimmer netting to date is multilayered monofilament line wide-mesh fish netting. It is almost invisible to the diver and difficult to avoid. When equipped with float sensors that detect large-scale movement, these nets have proven highly effective.
It would seem that a simple way of countering unknown frogmen or other divers would be for a police force or navy personnel to send their own frogmen to investigate. This is sometimes called counter-offensive frogmen. Combat divers undergo weeks of full-time underwater training, far more and harder than what most civilian sport divers undergo. They would be at full armed forces fitness before frogman training starts: see Frogman#Training. Superior underwater combat training would likely decide which two groups of frogmen would win. Generally, criminal or terrorist frogmen only have access to types of training which are available to civilians, or at least inadequate facilities.
Underwater combat between opposing teams of frogmen (although common in fiction (as in the movie Thunderball, and The Silent Enemy, and at least one incident in Sea Hunt), and often in comics) is unusual in reality.
Sometimes diving sea-police have arrested civilian divers for illegal spearfishing and diving in restricted areas and the like, and naval divers have been sent down to investigate unidentified divers in a naval harbour.
When confronted, sport divers are likelier to obey the patrol divers as ordered. Hostiles would be likelier to fight back.
Among the ways suggested of forcing arrested divers to surface would be attaching an inflatable float to each.:11
Objections to the likelihood of this tactic are:
If the patrol divers are riding suitable diver propulsion vehicles, they could travel faster and carry better weapons (lethal or non-lethal) and equipment for sonar search and navigation and communication, and perhaps a means (e.g. grab or net) to capture suspect divers in passing and tow them alongside back to the base or patrol boat.
It was thought expensive for a team of patrol divers to be on standby all the time kitted up to dive. France has police divers trained to arrest unauthorized or suspect divers underwater and to force them to surface. One common offence there is or was spearfishing while using breathing apparatus.
See Frogman#Equipment for features useful in equipment of frogmen who may get into underwater fights.
The Russian PDSS system is an example of an anti-frogman defence system which includes frogmen trained in underwater fights.
See Russian commando frogmen under "1970 and after" for a report of a real underwater fight between a guard squad of Russian PDSS frogmen and intruding enemy frogmen.
The films Above Us the Waves and The Silent Enemy are reconstructions of real World War II events, and each shows an underwater fight between opposing groups of frogmen, but those fights did not happen in the real events.
Some navies have thought underwater fights to be likely enough for them to design underwater firearms for frogmen to use as a lethal weapon. There is said to have been a real incident when Russian frogmen shot two anti-frogman dolphins.
These underwater firearms fire a steel rod, not a bullet, for better range underwater. They are all more powerful than a speargun, and can fire several shots before reloading. Their barrels are not rifled; the fired projectile is kept in line underwater by hydrodynamic effects, and is somewhat inaccurate when fired out of water.
A reported anti-frogman guard is (or was) dolphins trained to carry on the nose a device which injects a large amount of compressed carbon dioxide into the frogman. This would likely be lethal due to blood embolism. It is said that they were trained at Point Mugu. It was said that this device was abandoned because of fears that wild dolphins might imitate and start harassing ordinary divers. Today the mammals are primarily trained to force the diver to the surface using pushing techniques in the assumption that the majority of incursions can be addressed in this manner.
The US Navy has deployed sea lions to detect divers in the Persian Gulf. 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. 20 sea lions have been trained for this at the US Naval Warfare Systems Center in San Diego. Some have been flown to Bahrain to help the Harbor Patrol Unit to guard the US Navy's 5th Fleet. Sea lions adapt easily to warm water, can dive repeatedly and swim up to 25 mph, can see in near-darkness, and can determine the direction of underwater sound. In training the sea lions have been known to chase divers onto land. See also this link.
In 1970 to 1980 trained dolphins killed 2 Russian frogmen who were putting limpet mines on a US cargo ship in Cam Ranh bay in Vietnam. Subsequently, Russian PDSS frogmen were trained to fight back against trained dolphins. In an incident on the coast of Nicaragua PDSS frogmen killed trained anti-frogman dolphins. Arrival of underwater rifles and pistols seems to make the trained animal threat less.
Animals, unlike ROVs etc., need to be fed and kept in training whether they are needed at work or not, and cannot be laid aside in a storeroom until needed.
A ROV, as well as searching, could be equipped to arrest or attack divers on command, but with their technology as it is could not attack several targets one after another as quickly as a marine mammal. A surface-only ROV would need a long-range weapon to be effective against deeply submerged suspect divers.
Technology exists where underwater speaker systems can be deployed around the designated area. This array of speaker systems can be programmed to send high powered frequencies which then blasts powerful 'disruption' signals into the water. The frequencies have a maximum disorientation effect on the diver(s), which induce discomfort or panic causing them to leave the area or surface for interception. In cases where the divers remain in the water, the frequencies are likely to have a continued adverse effect which could cause sickness and confusion.
For sport divers and similar who have no means of covert entry, one method is merely to try to stop all divers from reaching water, or stopping them from using boats, in some particular place or area. Such a bylaw may be called for by the military to keep sport divers away from secret underwater sites, or by inshore fishermen to stop alleged poaching of shellfish.
The US has made many such regulations to protect such infrastructures as power plant and nuclear plant water intakes and discharges, bridge foundations, harbor and pier installations, and naval facilities.
The Socialist Federal Republic of Yugoslavia (until its demise) forbade all sport diving except a few Government-controlled groups, and required official permission for each campaign of archaeological or scientific diving.
The AN/WQX-2 is a diver-detector sonar used in anti-frogman precautions. It is in service with the US Navy. It uses Kongsberg Mesotech components. It can detect divers up to 2400 feet (= nearly half a mile) away.
The AN/WQX-2 finds range and bearing of the detected target relative to the sonar. The C3D console developed by SPAWAR converts this to a GPS position. It has software to distinguish diver echoes from shoals of fish, marine mammals, debris, bubbles from boat wakes, etc.APS underwater rifle
The APS underwater assault rifle (APS stands for Avtomat Podvodny Spetsialnyy (Автомат Подводный Специальный) or "Special Underwater Assault Rifle") is an underwater firearm designed by the Soviet Union in the early 1970s. It was adopted in 1975. Made by the Tula Arms Plant (Тульский Оружейный Завод, Tul'skiy Oruzheynyy Zavod) in Russia, it is exported by Rosoboronexport.
Under water, ordinary bullets are inaccurate and have a very short range. The APS fires a 120 mm (4.75 in) long 5.66 mm calibre steel bolt specially designed for this weapon. Its magazine holds 26 rounds. The APS's barrel is not rifled; the fired projectile is kept in line by hydrodynamic effects; as a result, the APS is somewhat inaccurate when fired out of water.
The APS has a longer range and more penetrating power than spearguns. This is useful in such situations such as shooting an opposing diver through a reinforced dry suit, a protective helmet (whether air-holding or not), thick tough parts of breathing sets and their harnesses, and the plastic casings and transparent covers of some small underwater vehicles.
The APS is more powerful than a pistol, but is bulkier and takes longer to aim, particularly swinging its long barrel and large flat magazine sideways through water.Cerberus (sonar)
Cerberus is an ultrasound Diver Detection Sonar to detect submerged divers. Mod 1 was made by Qinetiq, in their underwater business division. It was unveiled at UDT 2003. The underwater division was sold to ATLAS ELEKTRONIK UK in 2009 and the Mod 2 version was developed by them. It is semi-intelligent and reportedly can detect an air-filled chest cavity underwater and let its operator tell whether the echo is from a man or something irrelevant such as a seal or dolphin, and to distinguish between: a shoal of fish; a ship's wake; a diver with an open-circuit scuba set; a stealth diver with a rebreather; flotsam and jetsam.Diver detection sonar
Diver detection sonar (DDS) systems are sonar and acoustic location systems employed underwater for the detection of divers and submerged swimmer delivery vehicles (SDVs). The purpose of this type of sonar system is to provide detection, tracking and classification information on underwater threats that could endanger property and lives. Further, this information is useful only to the extent that it is made available to authorities in time to make possible the desired response to the threat, be it deterrent or defensive action. Subsurface threats are a difficult problem, because reliable detection is available to date chiefly by use of high-resolution active sonar or trained dolphins or sea lions.
The threat of an underwater terrorist attack is a concern to the maritime industry and port law enforcement agencies. Ports face a range of threats from swimmers, boat-delivered ordnance such as limpet mines and other forms of improvised underwater explosive devices.
DDS systems have been developed to provide underwater security for ports, coastal facilities, offshore installations, pipelines and ships. Due to the variety of life and objects that exist under the water, it is desirable that a DDS system be capable of distinguishing between large sea mammals, shoals of fish; a ship's wake; a diver with an open circuit scuba set and a stealth diver with a rebreather.
DDS systems have been developed that can be mounted on the seabed, on a pier or on the hull of a vessel. For complete port security these systems are integrated with the surface surveillance and security systems employed at ports, coastal facilities and offshore installations. Various systems provide specialized features to facilitate their use in port security systems including automatic detection features.Frogman
A frogman is someone who is trained in scuba diving or swimming underwater in a tactical capacity that includes police or military work. Such personnel are also known by the more formal names of combat diver, combatant diver, or combat swimmer. The word frogman first arose in the stage name The Fearless Frogman of Paul Boyton in the 1870s and later was claimed by John Spence, an enlisted member of the U.S. Navy and member of the OSS Maritime Unit, to have been applied to him while he was training in a green waterproof suit.The term frogman is occasionally used to refer to a civilian scuba diver. Some sport diving clubs include the word Frogmen in their names. The preferred term by scuba users is diver, but the frogman epithet persists in informal usage by non-divers, especially in the media and often referring to professional scuba divers, such as in a police diving role.In the U.S. military and intelligence community, divers trained in scuba or CCUBA who deploy for tactical assault missions are called "combat divers". This term is used to refer to US Army Special Forces (aka Green Berets) Combat Divers, Navy SEALs/Naval Special Warfare, operatives of the CIA's Special Activities Division, elements of Marine Recon, Special Amphibious Reconnaissance Corpsmen, Army Ranger Regimental Reconnaissance Company members, Air Force Pararescue, Air Force Combat Controllers, U.S. Coast Guard Helicopter Rescue Swimmers, United States Naval Search and Rescue Swimmers, United States Air Force Special Operations Weather Technicians, and the Navy Explosive Ordnance Disposal (EOD) units. In Britain, police divers have often been called "police frogmen".Some countries' tactical diver organizations include a translation of the word frogman in their official names, e.g., Denmark's Frømandskorpset; others call themselves "combat divers" or similar. Others call themselves by indefinite names such as "special group 13" and "special operations unit".Many nations and some irregular armed groups deploy or have deployed combat frogmen.Index of underwater diving
See the Glossary of underwater diving terminology for definitions of technical terms, jargon, diver slang and acronyms used in underwater diving
See the Outline of underwater diving for a hierararchical listing of underwater diving related articles
See the Index of underwater divers for an alphabetical listing of articles about underwater divers
See the Index of recreational dive sites for an alphabetical listing of articles about places which are recreational dive sitesThe following index is provided as an overview of and topical guide to underwater diving:
Underwater diving can be described as all of the following:
A human activity – intentional, purposive, conscious and subjectively meaningful sequence of actions. Underwater diving is practiced as part of an occupation, or for recreation, where the practitioner submerges below the surface of the water or other liquid for a period which may range between seconds to order of a day at a time, either exposed to the ambient pressure or isolated by a pressure resistant suit, to interact with the underwater environment for pleasure, competitive sport, or as a means to reach a work site for profit or in the pursuit of knowledge, and may use no equipment at all, or a wide range of equipment which may include breathing apparatus, environmental protective clothing, aids to vision, communication, propulsion, maneuverability, buoyancy and safety equipment, and tools for the task at hand.Kongsberg Mesotech
Kongsberg Mesotech Ltd, based in Port Coquitlam, BC, Canada, is informally operated by Kongsberg Gruppen. Website Proff.no does not include the company on the lists of subsidiaries of Kongsberg Gruppen or Kongsberg Maritime.
Mesotech make underwater surveillance and advanced frogman detection sonar systems.
The company was formed in 1973 to design and manufacture underwater acoustic equipment. Today Kongsberg Mesotech Ltd. supplies a worldwide customer base with a range of products for military, fisheries, oilfield, scientific, and other offshore market applications.Military diving
Underwater divers may be employed in any branch of an armed force, including the navy, army, marines, air force and coast guard.
Scope of operations includes: Search and recovery, search and rescue, underwater surveys, explosive ordnance disposal, demolition, underwater engineering, salvage, ships husbandry, reconnaissance, infiltration, sabotage, counterifiltration, underwater combat and security.Northstar Electronics
Northstar Electronics Inc. is based in Newark in Nottinghamshire in England.
Among other things they make underwater communications gear, and underwater diver-detection gear.Outline of underwater diving
The following outline is provided as an overview of and topical guide to underwater diving:
Underwater diving – as a human activity, is the practice of descending below the water's surface to interact with the environment.Underwater demolition
Underwater demolition refers to the deliberate destruction or neutralization of man-made or natural underwater obstacles, both for military and civilian purposes.Underwater warfare
Underwater warfare is one of the three operational areas of naval warfare, the others being surface warfare and aerial warfare. It refers to combat conducted underwater such as:
Actions by submarines actions, and anti-submarine warfare, i.e. warfare between submarines, other submarines and surface ships; combat airplanes and helicopters may also be engaged when launching special dive-bombs and torpedo-missiles against submarines;
Underwater special operations, considering:
Military diving sabotage against ships and ports.