Maritime attacks: detecting underwater terrorist threats

Increasingly sophisticated security measures over the past five years have made it difficult for terrorists to penetrate conventional international borders. This has forces terrorist organisations to look for new and innovative ways to strike their targets. With land and air defences becoming more difficult to breach, underwater attacks are now being considered.

In March, the Associated Press bureau in Manila reported that two Southeast Asian militant groups linked to Al-Qaeda were working together to train militants in scuba diving for seaborne terrorist attacks. The development was outlined in a Philippine military report obtained by AP that also noted increasing collaboration among Muslim militants in other areas, including financing and explosives.

Underwater security includes the ability to inspect, detect and identify anomalies on ships, bulkheads, piers and channel bottoms and to employ anti-swimmer technologies. Although waterside port security includes threat platforms found above the water - such as fast boats, jet skis, swimmers and canoeists - it is just as important to examine the potential threats posed by divers, submersibles and underwater scooters. Underwater swimmers can serve as an ideal means by which to covertly deliver explosives or a chemical or biological weapon, and those with propulsion assistance can carry as much as a 100 kg payload.

Richard Walker, a senior scientist at the US Coast Guard's research and development centre in Connecticut, told the 7th Marine Transportation System conference in Washington in November 2005: "We need to be able to detect and respond to potential hostile swimmers and divers in the port environment, and to be able to inspect ship hulls, piers and bulkheads to detect suspicious objects for further investigation, to enhance our awareness of port channels and bottom characteristics to minimise the threat of harbour mining."

New system

In February 2005, the US Coast Guard, which is the federal agency with primary responsibility for waterside security at US sea ports, unveiled a weapon to help it defend marine facilities. The Underwater Port Security System can detect, track, classify and intercept intruders, and allows for the inspection of hulls and pier structures. Due to its modular and portable design, it is capable of being deployed nationwide on short notice. The system is now being deployed to Coast Guard maritime safety and security teams throughout the country.

The primary threat that concerned the Coast Guard was the possibility of divers placing powerful explosives on the hull of a ship. The powerful sonar system scans the waters in and around a port, and then sends an alert to a land-based command centre about the presence of divers. A response boat then lowers a second sonar to confirm the discovery, sending back high-resolution images of any intruder.

Gary Hicks, vice-president for operations of the naval and maritime solutions business unit of research and engineering firm SAIC, pointed to the example of members of various terrorist organisations who receive training in underwater activities using scuba and re-breather technology.

Hicks noted that re-breather technology is available commercially and that training is available in many countries. Even marginally trained combat swimmers can be successful. For example, scuba-equipped members of the Liberation Tigers of Tamil Eelam (LTTE) have sunk many small Sri Lankan naval vessels using crude limpet mines, several of which were reputed to be in the 50 kg size range. To have a significant impact on most large vessels, a relatively large quantity of explosives needs to be carried, which presents logistical problems for the swimmer, especially in strong currents. Nevertheless, a strategically placed charge could cause damage and difficulties for cruise ships, naval vessels or even a single-hulled tanker. Larger explosive charges could theoretically be carried by underwater vehicles such as mini-subs.

SAIC has been working on countering this threat and has adapted a commercial high-frequency sonar for use in detecting and tracking swimmers in harbours. The company co-operated with several sonar diver detection companies and created a tactical system for detecting and tracking swimmers. The sonar data is also fused with other sensor data - such as radar, infra-red and video cameras and other special sensors - to allow for improved detection and a lower incidence of false alarms in harsh environments.

SAIC has also designed and patented a lightweight and rapidly deployable acoustic fence (also known as an underwater sentry), which automatically detects divers around ships and piers.

The acoustic fence has a string of small, very low-power active transducers that easily detect divers. Hicks said that tests carried out in San Diego harbour were successful, and they were able to easily distinguish between swimmers and marine mammals. The acoustic fence complements higher-cost, high-frequency diver detection sonar and can be combined with commercially available floating barriers to protect against both swimmers and small boats.

US lags behind

Others point out that improvements in underwater security in the US still lag behind those initiated in several other countries, including Singapore and Israel, which defend important installations against terrorist attack using a combination of patrols and randomly placed depth charges. Working with the Maritime and Port Authority of Singapore, one of the world's largest ports, a local company, Stratech Systems, has developed what it calls a vessel image-processing system, which brings together cameras, radar and underwater sonar, and automatically detects, identifies, tracks and predicts the movement of vessels passing through a waterway.

Israel's Rafael Armaments Development Authority is the country's largest firm engaging in research and development for the defence establishment. Rafael has developed two systems for the Israeli navy against the threat of diver intrusion. Both are incorporated into Rafael's Harbour Defence System and are currently being evaluated.

Underwater Intruders Detection and Alert System (UIDAS) is an acoustic active sonar system based on moored buoys deployed at a given distance (about 50 m to 100 m) between two successive buoys with a number of short-range sensors placed in a line to form a barrier. Each buoy consists of high-frequency, high-resolution, active sonar that can be set to fixed or selected search sectors. The buoys are connected via cable to a display and alert system situated in an on-shore command post. UIDAS can detect intrusions crossing this barrier.

Divers Detection Sonar (DDS) is a long-range detection sonar that is used for aerial coverage. Several DDS units can usually cover a complete area of a harbour. Because it is designed for long-range detection, it is useful for identifying larger threats such as swimmer delivery vehicles and Chariots (submersibles that can deliver commando or terrorist units to infiltrate harbours and other shore installations). The advantage of DDS over UIDAS is that it is able to provide an early alert and continue tracking once an alert is received.

Captain Zvi Yanai, a retired Israeli navy officer who is a research fellow at the Interdisciplinary Center (IDC) and a specialist in marine and homeland security, gave an overview of aspects of specific threats from underwater terrorism and countermeasures being taken. He said: "The perception of underwater terrorism still conjures up pictures of divers with oxygen tanks and fins, but the use of underwater mines aimed at shipping is a form of underwater terrorism." He explained that even when a ship enters or leaves a deep water harbour with a depth of 50 m or 60 m, a well-placed mine is capable of causing considerable damage. A mine in a strategic place could cause enormous damage to container ships and disrupt global trade.

Security experts point out that a sea port's water perimeter is frequently the most difficult to protect, in no small part because an attacker can enjoy the greatest element of surprise. Often the perimeter is the widest access point to the port and one that has no physical barriers for the entry or exit of ships, divers, swimmers or underwater vehicles, or for boats transiting from other parts of the port. The lines of authority on who controls the approaches to the port can also be murky, as is the delineation of responsibility between the ship and the port facility for monitoring areas around the ship.

Joe Charlaff is a freelance journalist who specialises in homeland security issues

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