The invention relates to the deployment of objects at sea, principally/ but not exclusively, to the deployment of mines.

Mines and other objects can be deployed at sea by aircraft, surface ships, submarines or small, self-propelled vehicles. Usu.ally minelayer shipsorconvertedcommercial shipssuchasferriesoroil supportvesselsare used. Themines are then launched from the shipby trolley or inclined ramp.

Navies are tending to use dedicated minelayer ships less, with the intention being to use converted commercial ships in times of hostilities. Such ships are vulnerable to attack, particularly in a period leading up to hostilities. Additionally, themajor proportion ofmineswill be carried in a very few shipsmaking the ρotenti»sl effect of the loss of even one shipvery heavy.

There is thus a need for a transportable container which is easily handled and safewhen towed even in extreme sea stateswhilst being suitable for carrying and deploying solid objects like mines.

The object of the invention is to provide an improved deployment systemforminesor other objectsenablingdelivery by ship, submarineor self propelled delivery unit.

The invention provides an object deployment unit comprising: a) a flexible tube shaped elongate body; b) means to releasably attach objects to the body; c) one or more ballast members; d) one or more buoyancy members; and e) means for automatic buoyancy compensation.

Thedeployment unit ispreferably suitablefor towingby surface ship or submarine, or for the inclusion of a motor to form a self-propelled delivery unit. Even relatively small vessels can usefully be used to tow such deployment units.

The unit canbe tewed on or below surface. Asurface shipcan tow it on the surface or depressed belowthesurface. Theunit canbedepressedby a kite or by an active depressor for example in the unit nose section. Such an active depressor eases handling of the unit and lessen the effect of environmental limiting conditions. A submarinewill tow the unit bel-ow the

surface and a mobile delivery unit can tow on or below the surface. Sub¬ surface tows are particularly useful for covert deployment of objects.

For submarineminedeploymentthetowedunithasmanyadvantagesover known forms. The submarine's defensive and offensive weapon stock is not depleted by carryingmines in torpedo storage areas. An alternativemethod of carryingminesby submarineusesbodybeltsaround the submarines. These have problems in that they increase the noise flow. Additionally there is the possibility of danger to the submarine from sympathetic detonations of the mines. The towed unit avoids these problems. The towed unit can, further, provide a launch platform for other weapons systems and thus complement the submarine's effectiveness.

An on-surface tow requirespositivebuoyancy, whereas a sub-surface tow requires negative but near neutral buoyancy.

A wide range of unit configurations is possible. Preferred arrangements, because of their simplicity of construction, are: a) a single line of objects in the body; b) a dual line of objects side by side in the body; or c) a surface raft of a plurality of bodies attached together. Anyconvenientnumber of units canbetowedbehindavessel ata time. The major component of the unit is in the form of ballast.

Preferably water filled sections, such as tubes, provide mass compliancy togetherwith neutral trim. At thetime ofpreparing the unit forarming and launch theballast tubes canbe initially air filled. Following launch, sea water can be pumped in to form the required ballast state.

Buoyancy members provide the displacement flotation to support the unit. Thesemaybe gas filled tubes, members of or containing compressible materials or members of or containing solid, non-compressiblematerials, as appropriate for the required uses of the unit.

Asurface towedunit shouldbepositively trimmed at all times. The resultant progressive increase in buoyancy as objectsare releasedmay cause problems and thus automatic compensation is preferablyprovided. This can be byventing air to reduce the flotation tubevolume and can advantageously be triggered electrically or mechanically e.g. by a snatch cord, following obj-ect release.

For a sub-surface tow the trim must be rapidly adjusted following weapon release to maintain the tow stability and reduce the risk of an accidental surface broach by the depleted unit.

Buoyancy compensation can be effected byventing air. However, for covert operation the noise emission and possible increase in target size generated by the expiration of buoyancy air must be minimised. Advantageously a non-venting buoyancy control isprovided. Preferablythis comprises a rigid flotation chamber having a first chamber containing a gas and a second chamber open to the water, the chambers being separated by a diaphragm or piston. Advantageously a piston is used and is held in a first position by a stopmeans with the first chamber filled with air when open to atmospheric pressure. As the unit moves deeper the water pressure increases, increasing the pressure in the second ch-amber. When the stop meansholding thepiston is releasede.g. whenanobject isdropped, thewater pressure causes the piston tomove, compressing the gas in thefirstchamber. A non-return catch and end stop can hold thepiston in position such that the increase in buoyancy caused by the dropping of the object is compensated for by the decrease in buoyancy from the compression of the gas in the first chamber.

Preferably the unit is fabricated from near neutral buoyant materials and so requires minimal compensation.

For sub-surface operation the unit is preferably arranged with a biεtatic trim. This has two trim states of positive and negative. The positive trim enables the unit to float on the surface, for example for initial attachment to the tewing vessel. The negative, preferably near neutral, trim is used during dived periods and reduces the likelihood of the unit broaching the surface when in transit or during stopped periods while submerged.

A bistatic buoyancy control preferably comprises a rigid flotation chamber having a first chamber containing a gas and a second chamber open to thewater, thechambersbeingseparatedbyadiaphragmorpiston. Preferably a diaphragm is used, which is supported by a differential spring that backs off the external hydrostatic pressure when shallower than a selected trim change depth, providing positive buoyancy, and is compressed by the increasing external hydrostatic pressure as the unit is tewed down through the selected trim change depth, thus compressing the gas and effecting the required displacement. Advantageously automatic passive trim changes can occur each time the unit passes through the selected trim change depth.

The payload compensation and bistatic buoyancy control devices can advantageously be combined into a single composite device.

Preferably the body and theballast and buoyancymembers are formed of flexible tubes.

Preferablytheassembledunit isencapsulated inastrong sheathwith a tapered nose and tail to reduce the hydro-dynamic form and skin drag. Conveniently the objects to be deployed aredistributed along the length of the body, advantageously within a body confine. Preferably the objects are attached by remotely activated release mechanisms. Advantageously the objectand releasemechanismsareaccessedfromaprogramandcontrol unitvia an umbilical central ccπrnunication spine, running the full length of the body. Preferably theprogramandcontrol unitisonboardthetowingvessel or included in a mobile delivery unit. Advantageously the program and control unit is a "carry aboard" unit for use on towing vessels.

Whenused forminestheprogramandcontrol unitpreferablytransmits mine targetting parameters immediatelyprior toweapon release, followed by automatic pre-release testing. The information is directed to the appropriate individually addressedmine bay. If there isapre-launchcheck failure, another mine can be substituted. This has the advantage that the unserviceable mine can be returned for maintenance, if desired or practicable, thus making this deployment arrangement more economic th»an systems wheremineshave tobe jettisoned if faultyto clear thelaunch rail. Further, the ability to address any mine along the unit eliminates the requirement for the mines to be embarked in their laying order.

The invention will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figures 1 (a) and (b) show an object deployment unit according tothe invention in cross-section and in plan view, as towed, respectively; Figures 2 (a) and (b) showanalternative configurationof an object deployment unit in cross-section and in plan view, as tow»εd, respectively; Figures 3 (a), (b) and (c) show, in cross-section, the loading of an object into a deployment unit; Figure4 shows incross-section, anobjectdeploymentunit suitable for surface towing; Figure 5 shows, in plan view, a multiple tow arrangement; Figure 6 shews in cross-section, a payload compensation buoyancy control unit;

Figure7 shows, incross-section, abistaticbuoyancycontrol unit; .and

Figure 8 shewsapayloadcompensationandbistaticbuoyancycontrol unit for Figures 6 .and 7 combined into a single unit.

As shown in Figure 1 an object such as a mine 1 is held in a sling 2 below two elongate ballast tubes 3a,b, by attachment means 5a,b. An umbilical spine 6 runs along one of the ballast tubes 3b and one of the attachment means 5b comprises a release mechanism that can be remotely activated via the umbilical 6, from the towing vessel 7. Pre-launch check signals can also be sent via the umbilical 6 to check the object 1 before release. A smooth sheath 8 encases a buoyancy tube4 and the ballast tubes 3 a,b, to provide a smooth outer surface.

Theballast tubes3a,b, are filledwithwater 9 toprovidea compliant supporting body that yields to impact, slides smoothlypast obstructions and follows the manoeuvres of the towing vessel 7 regardless of sea state. The buoyancy tube 4 is filledwith air 10 to provide buoyancy for thedeployment unit to compensate for the weight of the carried objects.

Figure 2 shows an alternative configuration of the deployment unit. Two lines of objects 1 are arranged side by side, held in slings 2 under ballast tubes 3 as shown in Figure 1. In this arrangement the air filled buoyancy tubes 4 are contained within the water filled ballast tubes 3. Further sections11 canbe addedtotheunit toforma raft typeunit of asmany lines of objects as is desired.

Figure 3 illustrates a method of loading an object 1 into the unit. The object 1 is attached to a support 12, such as a chain, suspended from, for exaittple, acrane (not shown) . Anelectrical cable13 connectstheobject1 to the umbilical 6. The object 1 is lowered (b) into the sling 2 below the two ballast tubes 3, containing buoyancy tubes 4. When the object 1 is in position the support 12 is released and theweight of the object 1 closes the ballast tubes 3 together (c) . A cover 14 closes the unit.

Figure 4 shows an object deployment unit that isparticularly useful for surface towing. It is formed in two sections that can be decoupled: a a transit section 15 and an object container section 16. The transit section 15 comprises three ballast tubes 3 and two buoyancy tubes 4 on a base 17. Sheath sections 18 enclose the sidesof the transit section15. On the topof the transit section is a rigid walkway 19 to enable aperson towalk along the unit if required. The objects 1 are held in the container section 16 by

attachments 20. Each object1 is connected to an umbilical spine 6bycables 13. Thecontainer section16 iscoupledtothetransitsection15 bycouplers 21a and b. A. drag reduction membrane 22 closes the base of the container section 16. The container section 16 can be used for storage of the objects andcan easilybecoupled to the transit sectionwith theaid of, forexample, a fork lift truck (not shown) .

Figure 5 shows a towing vessel 7, for ex»ample an ocean tug, towing multiple deployment units. Three units of a type previously described are tow»ed behind thevessel 7. Each unit includes adoubleline of objects1.and an umbilical 6 runs from the vessel 7, via the the towing lines 23 along the units and back via umbilical data links 24. This arrangement provides a secondary route for data communication in the event that one of the direct data links, 23a,b or c should fail.

Figures6, 7 and 8 illustratevariousbuoyancy control deviceswhich can be used to control the buoyancy of a sub-surfacetowed object deployment unit.

Figure 6 shows a simple payload compensationbuoyancy control unit. A rigid chamber 60 has an opening61 at one end. The chamber60 contains air 62 atatmosphericpressureandis sealedbyapiston63. Thepiston63 isheld inpositionbyapistonrelease64toprevent itmovingunderpressurefromthe surrounding water 65. The buoyancy control unit is attached to an object deployment unit of a typepreviously described andwhenanobject is released the piston release 64 is removed by a solenoid or pull cord (not shown) to allowthepiston63 tomove. Theexternalwaterpressureforcesthepiston64 tomovetocompresstheair62 inthechamber60. Apistonnon-returncatch66 andendstop67 holdthepiston63 inpositionwiththeair62compressed. The decreaseinbuoyancyfromthecompressionfortheair62 andthefillingofthe chamber60withwater65 compensatesfortheincreaseinbuoyancycreatedwhen an object is jettisoned from the unit.

Figure 7 shows a bistatic buoyancy control unit which allows increased buoyancy above a certain pressure level, to enable the unit to float, and allows a decreased buoyancy below that pressure level. In this wayautomaticpassivetrimchangesoccur eachtimetheunitpassesthroughthe differential depth. Thebuoyancy control unitcomprisesarigidchamber70 thathasanopening71 atoneend. Adiaphragm72 trapsair73 atatmospheric pressure in the chamber 70 (a). The diaphragm 72 is supported by a differential spring 74. When the unit is shallower than a selected trim

change depth 75 the spring 74 backs off the hydrostatic pressure from the surroundingwater 76 and the air 73 in the chamber 70 can expand (a). As the unit is taken below the trim change depth 75 the increasing external water pressure causes the spring 74 to collapse, compressing the air 73 and effecting the required displacement (b) . As the unit is brought back above the trim change depth 75 the spring 74 expands again allowing the air 73 to expand (c) (d) to increase buoyancy again.

Figure8 shows a combinedpayloadcompensationandbistaticbuoyancy control unit. Achamber 80 is divided into twoby a fixeddivider81 andhas two openings 82a,82b. Afirst side80a of the chamber is filledwith air 62 at atmosphericpressure. Asdescribed in relation toFigure6 apiston63 is held in position against external water pressure by a piston release 64. When released, thepiston 63 ismoved to a position heldbyanon-return catch 66 and end stop 67, compressing the air 62 between the piston 63 and the divider 81. A second side 80b of the chamber is also filled with air 73 at atmospheric pressure. The chaπber is sealed by a diaphragm72 supported by a differential spring 74 as described in relation toFigure7. In thisway changes of buoyancy due to depth changes or jettisoning of an object can be automatically effected by a single buoyancy control unit.

An object deployment unit according tothe invention isparticularly useful for transporting and deploying mines but can also be used for many other objects, for example position markers, εonobuoys, equipment, other weapons. In some arrangements, divers may be carried within a confine in the unit body and in this case the term "object" is taken to include divers or other personnel. It gives increased flexibility and effectiveness to object deployment vessels and minimal fitting out of towing vessels is required.