WO2010025951A2

WO2010025951A2 - Marine defence system

Info

Publication number: WO2010025951A2
Application number: PCT/EP2009/006477
Authority: WO
Inventors: Colin John Geoffrey Hillis
Original assignee: Colin John Geoffrey Hillis
Priority date: 2008-09-05
Filing date: 2009-09-07
Publication date: 2010-03-11
Also published as: WO2010025951A3; GB0816239D0

Abstract

A defence system for a marine asset such as a ship or an oil rig. The system comprises unmanned defence units, each unit comprising at least one weapon and being deployed with respect to the marine asset to create a defence perimeter at least partially around the marine asset. The defence units may be submersible and carry lethal or non-lethal weapons. The units may be self-propelled and may be capable of positioning themselves with respect to the marine asset and maintaining a desired position with respect to mobile marine assets.

Description

Marine Defence System

Field of the Invention

The present invention relates to marine defence systems.

Background to the Invention

Marine assets, such as vessels, oil rigs, gas rigs, renewably energy installations and the like, have been the target of attacks by terrorists. Known solutions to this problem include providing a military presence at the asset, and/or deploying unmanned aerial vehicles (UAVs) or unmanned surface vehicles (USVs) to patrol the surrounding area. These solutions can be expensive and are not always well suited to protecting marine assets that are stationary for long periods of time. Also, while these solutions can identify potential threats, they are often incapable of neutralising the threats. It would be desirable therefore to provide an improved defence system for marine assets.

Summary of the Invention

Accordingly, a first aspect of the invention provides an unmanned marine defence unit comprising a submersible body and at least one floatation device, the body being connected to said at least one floatation device by at least one line, wherein said body is separable from said at least one floatation device such that, in a deployed state of use, said at least one floatation device is locatable on the surface of a body of water while said submersible body is submerged in said body of water.

Alternatively, the unit is a surface-going vessel, or a surface-based structure, rather than being submersible. Accordingly, a second aspect of the invention provides an unmanned marine defence unit comprising a body adapted to be buoyant in water, especially seawater, and having one or more of the features described herein.

Preferably, said unit includes at least one weapon, typically at least one projectile weapon. In preferred embodiments, said submersible body carries at least one self-propelled underwater projectile weapon, especially a torpedo. The torpedo, or other projectile weapon, is preferably, but not necessarily, non-lethal. The torpedo, or other projectile weapon, may include means for guiding it to a detected target. The guiding means may comprise a sonar device. The torpedo, or other projectile weapon, may include means for generating an electrical or electronic pulse suitable for disabling electrical or electronic circuitry of the detected target.

In preferred embodiments, the unit includes means for communicating, preferably wirelessly, with a remote marine asset, such as a ship, oil or gas rig, renewable energy installation, port or other vessel or structure. The communication means may comprise an RF transceiver, or other wireless transmitting and/or receiving device, which may be located at said at least one flotation device or at said submersible body.

The unit preferably also includes a global position system (GPS) receiver, and optionally a GPS transmitter, which may be located at said at least one flotation device or at said submersible body.

One or more antennas may be provided for said communication means and/or said GPS receiver, as applicable. The or each antenna is preferably located on said at least one flotation device.

Preferably, one or more data communication cable is provided between said at least one floatation device and said submersible body for transmitting electrical data signals between said body and said at least one antenna. Said one or more data communication cable is preferably deployable and retractable, for example by means of a winch, or similar device, located on said submersible body or on said at least one floatation device. Alternatively, said one or more data communication cable takes the form of a resilient coil.

Said at least one line is preferably load-bearing, e.g. comprising a chain or cable. Said at least one line is preferably deployable and retractable, for example by means of a winch, or similar device, located on said submersible body or on said at least one floatation device. Alternatively, said at least one line takes the form of a resilient coil.

In preferred embodiments, said unit is self-propelled and includes propulsion means comprising, for example, one or more propellers coupled to drive means such as an engine or motor, and/or one or more propulsion jets. The propulsion means may be located at said least one floatation device but is more typically located on said submersible body.

The submersible body may include means for adjusting its buoyancy, for example one or more floatation chambers and means for selectably filling or emptying said chambers with ballast. Alternatively, said submersible body may be designed to be denser than sea water such that it sinks when separated from said at least one floatation device.

The unit preferably includes a control unit, typically located on said submersible body, for controlling the operation of the unit. The control unit is typically microprocessor or microcontroller based.

The unit preferably includes means for detecting remote targets, for example a sonar device and/or a radar device. The sonar device is best suited for location on said submersible body. The radar device is best suited for location on said at least one floatation device. In embodiments where the unit is self propelled, it is advantageously self- positioning with respect to a reference point. Conveniently, the reference point is located at the asset being protected, and may for example comprise co-ordinates identifying the global position of the asset. During use, the unit may be provided with a respective desired position relative to the reference point. Once launched, e.g. from the asset or elsewhere, the unit may determine its global position using the GPS receiver and compare this with the coordinates of the reference point. The unit may then propel itself until it determines that its global position is the desired position relative to the reference point. Advantageously, the unit checks its global position at intervals and so may determine whether or not it needs to move itself. Preferably, the unit is arranged to check, at intervals, the position of the asset by means of the communication link between them. To this end, the asset may also include a GPS receiver for determining its global position.

Alternatively, the unit may be self-positioning with respect to an absolute global position rather than a relative position.

In preferred embodiments, the submergible body submerges upon reaching its desired deployment position, leaving the or each flotation device on the surface of the body of water. In alternative embodiments, the body may submerge upon launch and subsequently travel to its desired position.

A third aspect of the invention provides a defence system for a marine asset comprising at least one of said unmanned marine defence units of the first and/or second aspects of the invention.

A fourth aspect of the invention provides a defence system for a marine asset, the system comprising a plurality of unmanned defence units, each unit comprising at least one weapon and being deployed with respect to said marine asset to create a defence perimeter at least partially around said marine asset. Further advantageous aspects of the invention will become apparent to those ordinarily skilled in the art upon review of the following description of preferred embodiments and with reference to the accompanying drawings.

Brief Description of the Drawings

An embodiment of the invention is now described by way of example and with reference to the accompanying drawings in which:

Figure 1 is a schematic plan view of a submersible defence system embodying one aspect of the invention;

Figure 2 is a schematic side view of a deployable submersible unit embodying another aspect of the invention and suitable for use with the system of Figure 1 ;

Figure 3 is an alternative schematic view of the unit of Figure 2;

Figure 4 is a schematic side view of the unit of Figure 2 shown resting on the seabed;

Figure 5 is a schematic side view of the unit of Figure 2 shown suspended above and anchored to the seabed;

Figure 6 is a schematic plan view of the submersible defence system of Figure 1 shown in an alternative deployment arrangement; and

Figure 7 is a schematic plan view of the submersible defence system of Figure 1 shown in a further alternative deployment arrangement. Detailed Description of the Drawings

Referring to Figure 1 of the drawings there is shown, generally indicated as 10, a marine asset defence system embodying one aspect of the invention. The system 10 includes at least one, but typically a plurality of, unmanned marine defence units in the preferred form of deployable submersible units (DSUs) 12 which embody another aspect of the invention. The DSUs 12 are deployed in use around a marine asset 14, for example a ship, oil or gas rig, renewable energy installation, a port or naval base, or any other vessel, structure or installation.

With reference to Figures 2 and 3, the DSU 12 is shown in more detail. The DSU 12 comprises a body 16, conveniently in the form of a platform, which carries a number of components as described in more detail hereinafter. In preferred embodiments, the DSU 12 is a vessel adapted for movement at least underwater but preferably also on the water's surface. To this end, the shape and configuration of the DSU 12, and particularly the body 16, is aerodynamically designed for efficient movement through water.

Preferably, the DSU 12 is self-propelled and includes means for propelling itself underwater and, preferably, along the water's surface. The propulsion means may take any suitable form, for example drive means such as an engine and/or motor coupled to one or more propellers, and/or propulsion jets. The propulsion means may be fixed, in which case a steering mechanism such as a rudder may be provided, or may be adjustable, e.g. pivotable, with respect to the body 16 to provide a steering function. In Figure 2, the DSU 12 is shown with two propellers 18 which are directionally adjustable to provide a steering function. An engine 20 for driving the propellers 18 is provided in, or on, the body 16. In this case, the body 16 may also include a fuel tank 22 for the engine, although in cases where the drive means is electrically powered this may be replaced by one or more batteries or other power source. In an alternative embodiment, the DSU 12 is not self-propelled. For example, in cases where the system 10 is to be deployed around an asset with fixed location, e.g. a port, there is no need for the units 12 to be self-propelled or self-positioning.

The DSU 12 includes means for communicating with the asset 14. Typically, the communication means is wireless and may for example comprise an RF (radio frequency) transceiver 24.

In preferred embodiments, the DSU 12 also includes means for communicating with a global positioning system (GPS), conveniently in the form of a GPS receiver 26. Optionally, the DSU may include a GPS transmitter (not shown). This can facilitate the asset 14, assuming that it is suitably GPS enabled, in identifying the global position of the DSU 12.

A respective antenna may be provided for the RF transceiver 24 and GPS transceiver 26, but in the illustrated embodiment they share a common antenna 28. The antenna 28 is preferably carried by a floatation device 30, e.g. a buoy, that remains on the surface 32 of the body of water 34 in which the DSU 12 is submerged during use. At least one data communication cable 36 is provided between the antenna 28 and the submerged portion of the DSU 12, or more generally between the floatation device and the submerged portion of the DSU 12, for the transmission of signals therebetween. The cable 36 may be retractable, in which case a reel or winch 38 may be provided on the body 16 (or floatation device) for gathering and deploying the cable 36. The winch 38 is preferably powered and this may be achieved by any suitable means, e.g. an electric motor (not shown). Alternatively, the cable 36 may be inherently extendible, for example taking the form of a resilient coil.

The GPS receiver/transmitter 26 and /or the RF transceiver 24 may be located on the submersible body 16 of the DSU 12 (as illustrated in Figure 3) or may be located on the flotation device 30 (as illustrated in Figures 4 and 5). A radar device (not shown) may also be provided. The radar device may be used to detect targets for disablement. Typically, the radar device is located at the floatation device 30. The radar device may share an antenna with the GPS receiver 26 and/or the RF transceiver 24, or may have its own antenna (not shown). The radar device may communicate with the submerged portion of the DSU 12 by means of cable 36, or other similar communications line (not shown).

Optionally, one or more further floatation devices 31 may be connected to the DSU 12 by means of one or more cables 37 or other line. The cable 37 is preferably retractable and may be deployable from winch 38, or from a separate winch (not shown). The flotation device(s) 30, 31 remain on the surface 32 during use and help provide stability to the DSU 12 while underwater as well as helping to maintain a desired depth beneath the surface 32. In addition, the floatation devices 30, 31 identify the location of the DSU 12. The data communication cable 36 is typically not strong enough to serve as a stabilising means for the DSU 12. Hence the cable 37 is preferably a load bearing cable or line, e.g. a chain. Alternatively, or in addition, the data cable 36 may be co- located with a load bearing cable. In the embodiments shown in Figures 4 and 5, only a single floatation device 30' is provided and so the data cable 36 and load bearing cable 37 are co-located.

One or more anchors 54 may be connected to the DSU 12 by means of one or more cables 56 or other line. The cable 56 is preferably retractable and may be deployable from winch 38, or from a separate winch (not shown). Depending on the depth of the water 34 and the length of the cable 37, the DSU 12 may rest on the seabed 58 as illustrated in Figure 4 (in which case the anchors are not necessarily required and may be omitted), or may be suspended above the seabed, as illustrated in Figure 5, in which case the anchor(s) 54 help to maintain the DSU's 12 position. In some embodiments, the DSU 12 includes means for controlling its buoyancy thereby allowing it to sink or rise in the water 34 as desired. To this end, one or more floatation chambers 40 may be provided in fluid communication with one or more tanks 42 for compressed gas, e.g. air. Each chamber 40 is capable of being flooded, conveniently with water from the surrounding body of water 34. To this end, a valve (not shown) may be provided for selectably opening the chamber 40 to the external environment. A valve (not shown) may also be provided for selectably allowing gas into the chamber 40 from the tank 42. The arrangement is such that introducing gas into the chamber 40 expels water from the chamber 40, e.g. by means of a non-return valve (not shown). Alternatively, the DSU 12 may be configured to be non-buoyant, in which case its position with respect to the water's surface 32 is determined by the length of the cable(s) or line(s) connecting it to the floatation device(s) 30, 31.

The DSU 12 further includes means for detecting objects in the surrounding water 34. Conveniently, this takes the form of a sonar device 44, although any other suitable technology may be used. As is described in more detail hereinafter, the DSU may have one or more sonar devices located on the body 16 and/or the torpedoes 46.

In preferred embodiments, the DSU 12 carries one or more self-propelled projectiles, or torpedoes 46. Optionally, the torpedoes 46 are non-lethal in nature, e.g. provide a ramming function rather than being explosive. Each torpedo 46 may include a guidance system 48 allowing the torpedo to be guided, for example by the DSU 12 or from the asset 14, towards its target. In addition the torpedo 46 may include means for delivering a disabling electrical pulse to a target. It is noted that the term electrical pulse is intended to embrace electronic pulse or other electromagnetic pulse that is capable of disabling electrical/electronic circuitry. Hence, the non-lethal weaponry may be said to include an electromagnetic weapon. The torpedo 46, guidance system 48 and/or electrical pulse generator 50 may be substantially conventional in design. It will be understood that the torpedo may additionally or alternatively include any other means (lethal or non- lethal) for disabling a target vessel. Further, any means (lethal or non-lethal) for disabling a target vessel, including the electric pulse generator, may be provided on the DSU 12 itself (on the submersible body or the floating part). In order that the DSU may act to disable vessels directly without the need to launch a torpedo. In some embodiments, therefore, the DSU 12 need no be armed with torpedoes.

The DSU 12 includes a control unit 52 for controlling the operation of the DSU 12. The control unit 52 comprises a suitably programmed microprocessor, microcontroller or other processing device (not shown). In particular, the controller 52 is programmed to receive instructions from the asset 14, or other remote source, and to operate the DSU 12 accordingly, and to report to the asset 14, or other remote destination, information concerning detected target objects and/or the status of the DSU 12. To this end, the asset 14, or other remote location, includes means for communicating, preferably wirelessly, with the or each DSU 12, for example an RF transceiver (not shown).

In embodiments where the DSU 12 is not self-propelled, it may be towed or otherwise transported to its deployment position by any convenient means. Non- self-propelled DSUs 12 are particularly suited for use where the asset 14 to be protected is stationary during use, e.g. an oil or gas rig.

In embodiments where the DSU 12 is self propelled, it is advantageously self- positioning with respect to a reference point. Conveniently, the reference point may be located at the asset 14, and may for example comprise co-ordinates identifying the global position of the asset 14. The or each DSU 12 is provided with a respective desired position relative to the reference point. Once launched, e.g. from the asset 14 or elsewhere, the DSU 12 determines its global position using the GPS receiver 26 and compares this with the coordinates of the reference point. The DSU 12 then propels itself until it determines that its global position is the desired position relative to the reference point. This is particularly useful in cases where the asset 14 is movable, e.g. a vessel, since it allows the DSU 12 to maintain its desired relative position as the asset 14 moves. To this end, the DSU 12 may check its global position at intervals and so determine whether or not it needs to move itself. The DSU 12 can also check the position of the asset 14 by means of the RF link between them. In this case, the asset 14 also includes a GPS receiver (not shown). Alternatively, the DSU 12 may be self-positioning with respect to an absolute global position rather than a relative position.

Upon reaching its desired deployment position, the DSU 12 submerges, leaving the or each flotation device 30, 31 on the surface 32. This may be achieved by appropriate flooding of the flotation chambers 40 and/or deployment of the cable(s) 36, 37, as applicable. In the preferred embodiment, the DSU 12 submerges under the control of its control unit 52 in response to determining that it has reached its desired position. Alternatively, in cases where the DSU is delivered to the desired location manually, its submersion may be effected by a human operator (not shown). In this case, an appropriate operating mechanism for the user is provided on the DSU. In alternative embodiments, the DSU may submerge upon launch and subsequently travel to its desired position.

When the DSU 12 needs to redeploy or is called back to the marine asset 14, it preferably rises to the water's surface 32 before travelling. This may be achieved by appropriate operation of the floatation chambers 40 and/or winch 38 as applicable. Alternatively, the DSU 12 may travel while the body 16 is underwater.

During use, the DSU 12 is able to communicate with the asset 14 by means of the RF transceiver 24. This communication may relate to, for example, deployment position, redeployment, ending deployment, calling the DSU back to the marine asset 14 and/or control operations such as the launch of torpedoes. The communication may comprise global position co-ordinates, radar locations and/or radio frequency communication of data. The sonar device 44 may be used for detection of targets by the DSU 12. Sonar technology may also be used to enable the torpedoes 46 to home in on the target, especially its propellers or engine. For example, a torpedo 46 may be guided to the approximate region of a detected target using its guidance system 48 and may subsequently be guided more precisely to the target by means of a sonar device (not illustrated) provided on the torpedo 46.

The torpedoes 46 may be substantially conventional in design. Lethal torpedo technology may be used instead of the abovementioned non-lethal torpedoes.

Alternatively, non-lethal and lethal torpedoes can be used together, e.g. each DSU 12 may be equipped with each kind of torpedo, or some DSUs associated with the asset 14 carry lethal torpedoes while others carry non-lethal torpedoes, to form security rings around the marine asset 14. For example, a plurality of DSUs 12 may be deployed to form two arrays, or rings, at least partially around the marine asset 14; an outer ring (for example bearing non-lethal torpedoes) and an inner ring (for example bearing lethal torpedoes). Should the non-lethal torpedoes fail to stop a target, then the lethal torpedoes can be deployed.

The electrical pulse generator 50 may use conventional electronic pulse emitting technology. In the preferred arrangement, the torpedoes 46 emit an electronic pulse just prior to the torpedo hitting its target. To this end, the torpedo may include means for activating the pulse generator 50 in response to determining that the target is within range of the torpedo. This may be achieved by providing the torpedo with a sonar device and a suitably configured or programmed on board controller, e.g. a microprocessor (not shown). Normally, the relatively small force needed to break the shear pin of small craft propellers will be provided by the ramming action of the torpedo on the propellers. However, as an additional disabling measure, the electronic pulse should disable the engine of the target craft. Alternatively, the electronic pulse may be emitted substantially simultaneously with the impact on the propellers. In such cases, the pulse generator may be arranged to emit the disabling pulse upon impact of the torpedo with the target, i.e. it may be include a shock or vibration activation device.

In preferred embodiments, the DSU 12 is able to offer protection without causing damage to craft legitimately in that area (possibly delivery craft or military/security craft). To this end, the DSU 12 may include means for detecting a disabling signal from a remote source, such as a vessel. For example, the disabling signal may be received by the RF transceiver 24 and antenna 28, the control unit 52 being programmed to recognise the received disabling signal. In response to detecting the disabling signal, the control unit 52 may be programmed not to take any offensive action at all while the disabling signal continues to be detected, or at least not to take any offensive action against targets detected in one or more specific regions while the disabling signal continues to be detected. These regions may be determined in any convenient manner, for example using the sonar, radar and/or GPS capabilities of the DSU 12 and/or the asset 14.

Alternatively, or in addition, the DSU 12 may be programmed to seek instructions from the asset 14 concerning whether or not to launch an attack.

Alternatively still, or in addition, legitimate small craft that will constantly be in the targeting zone (security or military craft) could use, for example, jet engines as opposed to propellers. The DSU 12 may be programmed to ignore recognised frequency signature(s) of legitimate craft. The DSU 12 may also be temporarily disabled by the asset 14 at any time. It is possible that the key to identification of friend or possible foe will be determined entirely or partially upon frequency signature of propellers.

The DSU 12 itself, and in particular the body portion 16, may be used directly as a projectile impact weapon to ram a detected target. To this end, the DSU may be provided with a ram 60. In this mode of use, the DSU 12 may be guided by any suitable means, for example its on board sonar and / or radar devices and/or by its GPS receiver 26. It will be apparent from the foregoing that one or more DSUs 12 are deployable to provide a defence system for the asset 14. Figure 6 shows a plurality of DSUs 12 deployed in a ring around a vessel 14'. Figure 7 shows an alternative arrangement in which the DSUs 12 are arranged to provide protection against attacks from the shore or from the sea. Upon detection of a valid target, the or each DSU 12 may take offensive action to disable or destroy the target. This action may be taken by the DSU 12 alone, i.e. a direct response to the detection of the valid target, or may be taken under the control of a signal received from the asset 14. For example, upon detection of a target, the DSU 12 may report the detection to the asset 14 and await further instructions before taking action. This allows a human operator (not shown) located on the asset 14 to evaluate whether or not to take offensive action and to instruct the, or each, DSU 12 accordingly.

It is advantageous although not essential that the DSUs 12 are submersed during use (except for the floatation devices 30, 31) since this helps to keep the DSU in position and remain more stable, especially in rough weather. When so deployed, the DSU 12 and keeps it in contact with the marine asset 14 being protected by means of the antenna 28 which is located above the water's surface. The DSUs can remain in this position as protecting layer around the marine asset and may check their position against that of the asset 14 at intervals to make sure they are in the correct position.

In preferred embodiments, the DSUs 12 use radar, GPS and/or other conventional tracking technologies to identify targets, especially small vessels, in unauthorised locations with respect to the asset 14. Alternatively or additionally, each marine asset 14 may have at least one human operator who can instruct the DSUs 12 to take offensive action based on their own opinion about an approaching vessel. This can be manually signalled to the DSUs in terms of GPS locations or radar information. Typically, torpedoes fired by the DSUs use the signalled target position to get them in the region of the target vessel. Once in that region, the torpedo can track down the vessel's propeller using sonar. Preferably, each DSU 12 is equipped with more that one torpedo and is capable of firing one or more torpedoes at a time.

The DSU 12 described above includes a submersible body. Alternatively, the unit 12 is a surface-going vessel, or a surface-based structure, rather than being submersible. The surface version of the DSU may have one or more of the features of the submersible version 12 described herein except those that relate solely to being submersible.

In an alternative mode of deployment, the units 12, which may be of the submersible or non-submersible type, are fixed to the asset 14, especially where the asset is a vessel. Typically a plurality of the units 12 are deployed around the exterior of the vessel and fixed to the vessel by any suitable means, e.g. a tow line, tether, or support structure. In such cases, the units 12 are arranged to interact with targets that are sufficiently far away from the vessel such that any electronic interference, explosion or other action taken by the units does not adversely affect the vessel that the units are protecting.

The invention is not limited to the embodiments described herein, which may be modified or varied without departing from the scope of the invention.

Claims

1. An unmanned marine defence unit comprising a submersible body and at least one floatation device, the body being connected to said at least one floatation device by at least one line, wherein said body is separable from said at least one floatation device such that, in a deployed state of use, said at least one floatation device is locatable on the surface of a body of water while said submersible body is submerged in said body of water, and wherein said unit further includes at least one weapon.

2. A marine defence unit as claimed in claiml , wherein said unit includes propulsion means located at said least one floatation device or on said submersible body.

3. A marine defence unit as claimed in 2, wherein said unit includes means for positioning itself with respect to a reference point.

4. A marine defence unit as claimed in 3, wherein said unit is arranged to position itself in use with respect to a marine asset to be protected.

5. A marine defence unit as claimed in claim 3, wherein said marine asset is mobile and wherein said unit further includes means for maintaining itself in a desired position with respect to said marine asset.

6. A marine defence unit as claimed in claim 3 or 4, wherein said positioning means includes a Global Positioning System (GPS) receiver.

7. A marine defence unit as claimed in any preceding claim, wherein the unit includes means for communicating, with a fixed or mobile marine asset.

8. A marine defence unit as claimed in claim 7, wherein said communication means comprises a wireless transmitting and/or receiving device located at said at least one flotation device or at said submersible body.

9. A marine defence unit as claimed in any preceding claim, further including a global position system (GPS) receiver, and optionally a GPS transmitter, which may be located at said at least one flotation device or at said submersible body.

10. A marine defence unit as claimed in claim 9 or 10, further including one or more antennas for said communication means and/or said GPS receiver, the or each antenna preferably being located on said at least one flotation device.

1 1. A marine defence unit as claimed in any preceding claim, wherein one or more data communication cable is provided between said at least one floatation device and said submersible body for transmitting electrical data signals between said body and said at least one antenna.

12. A marine defence unit as claimed in claim 10, further including means for deploying and retracting said one or more data communication cable.

13. A marine defence unit as claimed in any preceding claim, wherein said at least one line is load-bearing, the unit preferably further including means for deploying and retracting said at least one line.

14. A marine defence unit as claimed in any preceding claim including at least one projectile weapon.

15. A marine defence unit as claimed in claim 14, wherein said submersible body carries at least one self-propelled underwater projectile weapon, especially a torpedo.

16. A marine defence unit as claimed in claim 15, wherein said projectile weapon includes means for guiding it to a detected target.

17. A marine defence unit as claimed in any preceding claim wherein said at least one weapon includes at least one non-lethal weapon.

18. A marine defence unit as claimed in claim 17, wherein said at least one non- lethal weapon comprises an electromagnetic weapon capable or delivering an electromagnetic pulse for disabling electronic systems.

19. A marine defence unit as claimed any preceding claim, wherein said submersible body includes means for adjusting its buoyancy, for example one or more floatation chambers and means for selectably filling or emptying said chambers with ballast.

20. A marine defence unit as claimed in any one of claims 1 to 18, wherein said submersible body is arranged to be denser than sea water such that it sinks when separated from said at least one floatation device.

21. A marine defence unit as claimed in any preceding claim, further including a control unit, typically located on said submersible body, for controlling the operation of the unit.

22. A marine defence unit as claimed in any preceding claim, further including means for detecting remote targets, for example a sonar device and/or a radar device.

23. A marine defence unit as claimed in claim 22, wherein said sonar device is located on said submersible body.

24. A marine defence unit as claimed in claim 22 or 23, wherein said radar device is best suited for location on said at least one floatation device.

25. A defence system for a marine asset, the system comprising at least one marine defence unit as claimed in claim 1 deployed with respect to said marine asset in order to create a defence perimeter at least partially around said marine asset.

26. An unmanned marine defence unit being deployable with respect to a marine asset, wherein said unit includes at least one weapon, means for propelling itself and means for positioning itself with respect to said marine asset.

27. A defence system for a marine asset, the system comprising a plurality of unmanned defence units, each unit comprising at least one weapon and being deployed with respect to said marine asset to create a defence perimeter at least partially around said marine asset.