Anti-frogman techniques
From Wikipedia, the free encyclopedia
This article is about protecting craft and bases and installations that can be accessed from water, from intrusion by frogmen or other divers that may be a security threat.
This need was shown by the achievements of World War II frogmen.
After that, public availability of sport scuba gear has caused real or supposed needs in some places for underwater security of valuable underwater objects and underwater archaeology sites and of shellfish fishing stocks.
In most scenarios nowadays the intruders will likeliest be civilian sport divers, or former civilian sport divers who have turned to work diving, but in war or semi-war conditions they may be enemy frogmen attacking or spying. A police-type technique that is reasonably safe on land may be risky to a scuba diver. The USS Cole bombing showed that fast decision is needed sometimes; the port guards cannot always afford to wait and see what the intruder does, as a diver swimming at 1 mph would move 88 feet in a minute, or 110 feet (the length of a USCG Patrol Boat) in 1.25 minutes.
The MSST (Maritime Safety and Security Team) is a United States Coast Guard harbor and inshore patrol and security team whose methods include detecting submerged divers.
Contents
|
[edit] Sport divers and underwater security
Keeping underwater security against frogman intrusion has been complicated by the expansion of sport diving since the mid 1950's, 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 beause any genuine reports of intruders would be swamped in ever more reports of civilian sport divers who are not in military areas.
For a long time it would be easy for men who know about diving to distinguish a sport diver with an open-circuit scuba such as an aqualung from a combat frogman with a rebreather. Also, 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.
However, particularly in former years when scuba diving was less common, many non-divers including police etc know little about diving and do not know of this difference in kit, but describe 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 actually ordinary sport scuba gear.
After about 1990 the multiplication of makes of sport diving rebreather have clouded this distinction, and advanced sport divers increasingly tackle longer deeper more dangerous dives using equipment once available only to professionals. This means that even "less-lethal" techniques for trapping them underwater, disorienting them, or (especially) forcing them to the surface pose an ever-increasing risk to civilian lives.
In former times civilian diving was only for work and needed Standard diving dress and big easily-seen surface support craft, but sport scuba diving has changed that.
Some naval people object to civilian divers getting into waters being used for armed forces exercises, or treat any sport diving as intruding into naval and work divers' territory.
Another result of sport diving is a risk of civilians independently re-developing, and then using or selling without secrecy cover, technologies until then kept as military secrets, such as technical advances in underwater communications equipment. (For a loss of military secrecy caused by independent civilian duplication (though not underwater), see Exocet#The Lokata.)
There have been incidents which have demonstrated poor underwater security, 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 below under #Prevention.
On a very small scale, the definition of "anti-frogmen defense" could be stretched to include incidents when inshore shellfish fishermen, with or without legal backing or permission, tried to keep out or restrict visiting scuba divers which they saw as an alleged threat to shellfish stocks or otherwise adversely affected the work of those fishermen.
[edit] Detection
[edit] On the surface
A man on the surface of the water is liable to detection by the same means as used on land, e.g. eyesight, surveillance cameras, thermal imaging, radar.
[edit] Relying on eyesight from land or from surface patrol boats
In World War II this was the main precaution. That is why World War II manned torpedo operations tended to happen by night around new moon when there is the least amount of moonlight.
Open circuit scuba bubbles can make detection easy, but not easily in rough foamy sea water.
Swimming deep can hide from surface guards; but if the underwater visibility is good, he may have to go deeper than is safe with an oxygen rebreather, and with open circuit scuba he makes more bubbles at each breath.
Thermal imaging could detect a diver near or at the surface, but not so easily in warm tropical water.
[edit] Millimeter wave detection
Detecting electromagnetic signals in the 27 to 200 Ghz range may improve detecting surface swimmers at night, but this idea is not yet tested. [1](page 5).
[edit] Ultrasound detection
Artificial intelligence and electronic neural networks and developments in ultrasound have made possible specialized diver-detector sonars.
Experience has showed that passive sonar (i.e. merely listening for underwater noises) cannot detect everything; in particular it cannot easily detect rebreather divers and unequipped surface swimmers; and it can detect direction, but not distance unless readings from two or more listening stations can be correlated.
High-power low-frequency sonar commonly used for depth sounding and to detect large objects (including submarines) is not good at detecting small obects like divers, but in the US Navy Diving Manual 24 is defined as hazardous to divers. [2](page 3)
Examples of diver-detecting active sonar systems are:-
[edit] UPSS
The UPSS is Underwater Port Security System. It is composed of underwater patrollers and computerized sonar and anti-diver ultrasound weapons. It is made in the USA. See Underwater Port Security System. (See also this link).
[edit] Cerberus
This is a blue egg-shaped ultrasound device to detect submerged divers. It is made by QinetiQ. It can distinguish a diver from a seal or dolphin or porpoise. Its range is about 700 meters. It was unveiled at UDT2003. 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's or something irrelevant such as a seal's or dolphin's, 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. See this link.
QinetiQ pages about Cerberus:-
- About Cerberus, protecting oil rigs
- Swimmer Detection System (SDS) Cerberus 360
- Cerberus provides diver detection includes image
- Cerberus - Protecting ships and naval assets from attack
- Cerberus protects against attack on oil industry infrastructure
- QinetiQ displays innovative solutions at maritime exhibition
- QinetiQ’s Cerberus protects America’s Cup
- Big image of a Cerberus unit
- A Cerberus unit in a private yacht
[edit] Northstar
Northstar Electronics (which see) make a type of diver-detector sonar.
[edit] AN/WQX-2
AN/WQX-2 (which see) is a type of diver-detector sonar. The US Navy uses it.
[edit] Trained animals
Trained dolphins and sea lions can find submerged divers. Both can see, and hear direction of sound, well underwater, and dolphins have natural sonar. [3](page 3).
The U.S. Navy’s MK6 Marine Mammal System is supported by SPAWAR and uses dolphins to find and mark mines and divers in the water. This system was used in:-
- Vietnam in 1970-71.
- Persian Gulf in 1987-1988.
- San Diego harbor for security during the 1996 Republican National Convention.
But they only have one team. [4](page 11).
[edit] Surveillance of civilian divers
This link claims 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 is now done annually.
[edit] Anti-frogman weapons
Some anti-frogman weapons, and weapons that come to mind when wanting to defend against frogmen, are:-
[edit] Police-type non-lethal weapons
These may be useful when assault-boarding a boat, but not often otherwise.
- Mace and pepper spray may make an unequipped surface swimmer drown, and are useless against a man with a diving mask and breathing set whether he is in or out of the water.
- Tasering a surfaced diver would either be insulated off by his rubber diving suit, or may make him panic and drown, including making him lose his scuba mouthpiece if any. Any electric-shock weapon can be shorted out by water.
- Bean bag rounds, rubber bullets, pepper balls, and similar would be stopped in a few inches by water.
[5](page 9).
[edit] Depth charge
A depth charge is effective, 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 commonsense 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 the diver.
[edit] Light
Dazzlers are much less effective underwater than on land. [6](page 17).
[edit] Sound
There has been much research about the effect of sound on divers. See the bibiography in [7](page 51 etseq, 356 entries}.
High intensity sound 20-100 Hz, & high intensity impulse noise, are promising. More testing is recommended, according to this link(page 47).
The sound generated by a plasma sound source is promising as an irritant noise, according to this link(pages 42-43).
[edit] Ultrasound
The main effects of ultrasound on the human body are heating and cavitation. See [8](pages 21-23) for detailed information. Also see ultrasound and sonic weaponry.
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-pressue part: this is cavitation and can cause injury.
One well-known method is a powerful blast from a military ship's ordinary search sonar, 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 bow mounted, so a diver attacking at the stern would be in the sonar baffle region, and unaffected. High-power low-frequency sonar commonly used for depth sounding and to detect large objects (including submarines) is not good at detecting small obects like divers, but in the US Navy Diving Manual 24 is defined as hazardous to divers.[9](page 3)
Most ships, both military and non-military, carry smaller "navigation" sonars such as depth finders or collision sensors, however their high frequencies and relatively low power lack effectiveness against divers.
Around the 1970's there were reports among sport scuba divers from offshore from a Ministry of Defence area in Dorset in England of diver deaths, mass deaths of fish, and divers returning reporting "strange sonic noises"[citation needed]: they speculated about a secret anti-frogman weapon, but it may have been merely a powerful modulated ultrasound beam intended to communicate with submarines.
Some say that these speculations are mostly fanciful and that since the human body is very close to the impedance as 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.
Most deaths of people in the water from sonar have come from a freak combination of diver physical condition, and local acoustic reflection effects of high powered audible sonar that uncharacteristically "focused" the sound on the hapless diver, or precisely matched the resonant frequency of the diver's air cavities.[citation needed]
However:-
- Early researchers into underwater ultrasound soon found that small water animals sometimes died if caught in ultrasound beams.[citation needed]
- This method of attack occurs in nature; it has been proved that some toothed whales can make and focus audible sound "clicks" so powerful that the whale routinely uses it to stun prey at close range.[10] [11]
- Non-Lethal Swimmer Neutralization Study section 5.2 (page 18 etseq) describes the effect of ultrasound on scuba divers.
- The UPSS/IAS diver-detecter sonar system includes an underwater shockwave emitter: see Underwater Port Security System.
It is unknown what later proof or disproof there has been of speculations such as appeared in a book about Cousteau written by Diolé 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.
[edit] Audible sound
[edit] To cause discomfort to the diver
The sound may be a sort that irritates or causes pain. [12](page 27, 28}
[edit] Verbal
The sound may be an order to surrender or surface or go onshore or to the 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.
[edit] Sensitivity to the sound
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 1000Hz and 5000Hz. This may affect ability to understand speech.
Research showed that, at depths up to at least 30 feet, divers' wetsuit hoods lowered underwater hearing sensitivity by 10 to 35 decibels at 1000 Hz and above, and by little or nothing at 250 Hz and below.
Underwater, humans are much less able to tell which direction a sound came from. Research showed that what ability remains is better with bang!-type noises than with pure tones. [13](page 28}
[edit] Low frequency
Research showed that loud sound at 100 to 500 Hz caused vibration, and at high powers cavitation and damage. [14](pages 32-35).
[edit] Infrasound
[15] section 5.2.5.5.1 (page 32 etseq) describes the probable lack of effect of infrasound on divers.
[edit] Electric shock
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.
[edit] Mechanical devices to capture submerged divers
Such devices occur in fiction, commonly in comics. Some sorts might be possible if designed.
The grab and suction types would likely be mounted on a dredging-type craft or a small submarine, and (according to type) might be also used for small-scale dredging or to recover submerged objects.
[edit] Net
A net can sometimes be used to catch submerged divers. [16](page 3). This agrees with talk among diving circles about a fishing trawl being the handiest way for naval men to get unwelcome or unauthorized divers out of the water.
This link describes a case of it happening accidentally.
[edit] Grab
This type has been seen in fiction.
A text fiction story (The Deep Range by Arthur C. Clarke) mentioned a diver-catching grab used to recover a work diver suffering from nitrogen narcosis, not to arrest a suspect.
Grab-type devices on various scales are very commonly used in nature underwater by animals. The device is usually its jaws, but in some animals evolution converted legs into arms to handle objects; see Opabinia for a very early example of a nose turned into a grab.
[edit] Suction
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.
This has happened in reality as a diving accident among work divers (e.g. being sucked against a water outlet, or accidents in suction dredging.)[citation needed]
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 have a strong suction component to the way they work.
[edit] Anti-swimmer barriers
[edit] Rigid full-depth netting
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. [17](page 14 etseq)
[edit] Safe Barrier
This make 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 a Swedish company, Safe Barrier Systems (SBS), a division of NCC Stockholm. It is rigid metal netting, covered in polyethylene electrical insulation, and polyurethane abrasion protector outside that. The strands are electrified so that any frogman attack on the net will be detected by that strand going open-circuit (not to electrocute him). The grid size best suited to deter divers is 250 x 250 mm = 10 x 10 inches. Testing in the UK showed that a diver using bolt cutters could cut a hole big enough to swim through in 60-90 seconds.
It was found that the net could be evaded by climbing over it, or getting under it, or by using a wire loop to complete the circuit where he cuts each strand.
The net system can be equipped with a gate (operated by an air compressor), to allow traffic in and out of the protected area.
SBS currently supports 15 sites: including four with gates, but they are not making this net system now, due to lack of demand. The price quote for a new net was more than $7,000,000.
[edit] F-8000
This make is or was made by BEI Security Systems. Its system that alarms if cut is fiber-optic.
[edit] Aquamesh
This made was made by a U.K. company. Its system that alarms if cut was fiber-optic. This make seems to have disappeared, and the tradename "Aquamesh" is now used for underwater wire mesh used in the aquaculture industry for lobster and crab traps.
[edit] Floating barriers
These will stop surface boats from dropping divers in unwelcome areas. [18](page 14 etseq)
[edit] Flexible full-depth netting
One effective anti-swimmer netting to date is multilayered monofilament line wide-mesh fish netting. It is almost invisible to the diver and hard to avoid. When equipped with float sensors that detect large-scale movement, these nets have proven highly effective.
[edit] Sending other frogmen against them
It would seem that often a simple way of countering unknown frogmen or other divers would be for a police force or navy base personnel to send their own frogmen to investigate. Combat divers undergo weeks of fulltime underwater training which vastly contrasts with the amount of aquatic training the average civilian sport diver undergoes; and they would be at full armed forces fitness even before the frogman training starts: see Frogman#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.
When confronted, sport divers are likelier to follow the patrol divers quietly as ordered; hostiles would be likelier to fight back.
Among the ways of forcing arrested divers to surface would be attaching an inflatable float to each.
Objections to the likelihood of this tactic are:-
- It may result in an underwater knife fight, risky to both.
- Risk of both drowning because of both sides atacking the others' breathing sets
[19](page 11).
- This risk to the patrol divers depends on the design and resistance to damage of their equipment.
- It may be difficult for the patrol divers to find the suspects; but this depends on:-
- Underwater visibility, which can be from a few inches (as sometimes in British sea) to 100 feet (as often in the tropics).
- Light level.
- It may be easier if one of the patrol divers has a hand-held sonar of the type that has a screen, e.g. the INSS;
- or if a trained sea mammal leads the patrol divers to their target.
- 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 spearfishing while using breathing apparatus.
Large underwater fights between two squads of opposing frogmen have been seen at least three times in fiction films (Above Us the Waves, Thunderball, and The Silent Enemy), but there is not much accurate information on what combat between frogmen (or between other divers) underwater has happened in the real world (except for small-scale police-type arrests, for example as described in the previous paragraph).
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.
[edit] Underwater firearms
Some navies have thought underwater fights to be likely enough for them to design underwater pistols and rifles for frogmen to use; there is said to have been a real incident when Russian frogmen with SPP-1 Underwater Pistols shot two anti-frogman dolphins.
[edit] Trained animals
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. 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. But see http://www.flagshipnews.com/archives_2003/aug212003_11.shtml for dolphins used as an anti-frogman patrol. 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.
This link says that 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 tell where sound comes from underwater. In training the sea lions have been known to chase divers onto land. See also this link.
This link reports that in 1970 to 1980 trained dolphins killed 2 Russian frogmen who were putting limpet mines on a USA cargo ship in Cam Ranh bay in Vietnam. After that, Russian PDSS frogmen were trained to fight back against trained dolphins, and 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.
[edit] Remote-controlled underwater vehicle
A ROV culd search dor submerged divers; but ROV's are expensive to run, and could not attack several targets one after another as quickly as a marine mammal. [20]](page 13)
[edit] Underwater ROV
An underwater ROV needs to be controlled. It could find and identify divers, and perhaps deter them. It should not be easily overpowered or attacked or outpaced by the suspect divers. If it is to attack the suspects, it should carry a suitable weapon.
[edit] Surface ROV
A surface ROV can move on its own, but without a long-range weapon can do little against deeply submerged suspect divers.
[edit] Prevention
[edit] Preventing public access to frogman-type diving gear, or to any diving gear
- Siebe Gorman had a policy in Britain until around 1956 of keeping prices of aqualungs too high for most civilians to afford; legal restrictions on exporting currency stopped people from importing cheaper foreign aqualungs. See Timeline of underwater technology#Public interest in scuba diving takes off for how this barrier broke down.
- The Subskimmer, which is useful for covert underwater penetration, took decades to develop and passed through at least three firms and is still too expensive for sport divers and sport diving centers. This may be due to interference from Ministries. Or it could have been a commercial decision: the market for sports use was judged to be too small.
- Siebe Gorman consistently refused to sell rebreathers to the civilian public. Mixture rebreather development was kept away from the public eye and the sport scuba trade until the end of the Cold War in 1991.
- In the U.S., military rebreathers were not marketed to the public primarily due to cost and attendant legal liability issues. Legal issues still tend to discourage the development and sale of the rebreather in the U.S., though acceptance and use is increasing. The U.S. military has not tried to stop sale of rebreathers to the public to the U.S., as it has realized that recreational SCUBA has now exceeded earlier military SCUBA in quality, and holds hope that a similar increase in quality and decrease in price will come from commercial-off-the-shelf rebreather equipment.
[edit] Preventing public access to diving water
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 instigated by the military to keep sport divers away from secret underwater sites, or by inshore fishermen to stop alleged poaching of shellfish. The U.S. has instituted 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.
[edit] External links
- Non-Lethal Swimmer Neutralization Study, released by Waterfront Physical Security, about 3 megabytes, PDF format, 82 pages, images. Contents:-
| sec | page | title | summary & references |
|---|---|---|---|
| ii | Administrative information | "This document is not copyrighted", etc | |
| iii | Executive summary | ||
| 1 | 1 | The need for a non-lethal response | to diver intrusion was highlighted by the USS Cole bombing. |
| 2 | 3 | Detection | Active sonar is needed, as passive sonar is not fully effective. And see #Detection. |
| 3 | About the US Navy's AN/WQX-2 swimmer-detection sonar, with images. | ||
| 3 | 7 | Search parameters | Which devices are suitable?, since many intruders will be innocent sport divers. |
| 4 | 9 | Existing in-air approaches | About various anti-riot and similar devices which are routinely used on land. |
| 4.1 | 9 | Projectiles | Bean bag rounds, rubber bullets, pepper balls, & similar are not suitable. |
| 4.2 | 9 | Chemical agents and electrical devices | Mace & pepper spray may drown surface swimmer, useless against scuba. |
| 10 | Tasers are not suitable except perhaps on surface within 15 feet of the boat, & then risky. | ||
| 4.3 | 10 | Physical force | by patrol divers; and see #Sending other frogmen against them. |
| 11 | by trained dolphins or sealions; snd see #Trained animals. | ||
| 12 | Sending an ROV down to look for the suspect divers. | ||
| 4.4 | 14 | Restraints | Net barriers; and see #Anti-swimmer netting. |
| 5 | 17 | Light- and sound-producing devices | |
| 5.1 | 17 | Light-producing devices | intended to dazzle. May cause epilepsy. Less use under water. |
| 5.2 | 18 | Sound-producing devices | A table |
| 5.2.1 | 19 | Acoustics terminology | An equation and a table |
| 5.2.2 | 20 | Which bioeffect? | Which effect on the suspect diver's body to aim for?; a table & science |
| 5.2.3 | 21 | Ultrasound | And see #Ultrasound weapon & Sonic weaponry#Lethal sonic weapons, underwater. |
| 5.2.4 | 23 | Infrasound (1-20 Hz) | No definite result yet; probably no use. |
| 5.2.5 | 25 | Audible sound | And see #Audible sound: irritating, or painful, or verbal orders. |
| 5.2.5.1 | 26 | Diver hearing | About divers' ability to hear underwater. A graph. |
| 5.2.5.2 | 26 | Fetal studies | Effect on fetuses. |
| 5.2.5.3 | 29 | Hearing-related bioeffects | Research on making noises irritating. |
| 5.2.5.4 | 30 | Acoustic deterrent devices used by fish farms | to keep seals away. |
| 5.2.5.5 | 31 | Extra-aural bioeffects | Effect of audible sound other than on the ears. |
| 5.2.5.5.1 | 32 | Low frequency (100-500 Hz) | Long description of research results. |
| 5.2.5.5.2 | 35 | Extra-aural bioeffects in humans | Including results of experiments on submerged divers. |
| 5.2.5.5.3 | 37 | Very low frequency (20-100 Hz) | Description of research results. |
| 5.2.5.6 | 40 | Impulse noise (startle response) | Research results |
| 5.2.5.6.1 | 42 | Plasma sound source | Noise from an underwater spark gap. Not a magic frequency like Star Trek "phaser on stun", but it seems promising. |
| 6 | 45 | Electromagnetic devices | The Active Denial System does not work underwater. Magnetic field generator to make a suspect diver's compass misread is considered. |
| 7 | 47 | Towards a non-lethal swimmer deterrent device | High intensity sound 20-100 Hz, & high intensity impulse noise, are promising. More testing is recommended. |
| 8 | 49 | Summary | Recommends: Visible patrol boats & barriers to deter sport divers & similar. Audio commands to submerged divers. 20-100 Hz sound. |
| 9 | 51 | Bibliography | has 356 entries. |
