WO2008125809A1

WO2008125809A1 - A payload deployment system

Info

Publication number: WO2008125809A1
Application number: PCT/GB2008/001230
Authority: WO
Inventors: Bryan Jeffrey Owen; Dale Michael Jeffreys; Peter David Clarke; Jeremy William Smith
Original assignee: Strachan & Henshaw Limited
Priority date: 2007-04-11
Filing date: 2008-04-08
Publication date: 2008-10-23
Also published as: GB0707008D0

Abstract

The application discloses a payload deployment system for a marine vessel. The system includes an ejection tube (2) for holding a payload (1) and an ejection element (25) in the ejection tube (2), the ejection element (25) being moveable in the ejection tube (2) and being arranged releasably to engage the payload (1). The system also includes a propulsion system (36, 37) for moving the ejection element (25), the propulsion system having an electric motor with a moveable first part. A cable (32) extends between the propulsion system (36, 37) and the ejection element (25). Movement of the first part of the electric motor is arranged to cause movement of the cable (32) which causes movement of the ejection element (25) in the ejection tube (2), thereby to eject the payload (1) from the ejection tube (2).

Description

A payload deployment system

Background of the Invention

The field of this invention relates to systems for deploying payloads from vessels, e.g. submarines, and in particular, systems for launching stores (e.g. torpedoes) from submarines .

Summary of the Prior Art

Conventional torpedo launch systems utilise fluid pressure to force a torpedo from a torpedo launch tube. An example of a known torpedo launch system is described in European Patent No. EP 0526831 B. The system includes a torpedo launch tube, in which a torpedo is located prior to launch. A piston tube is provided adjacent the torpedo launch tube, the piston tube having a piston therein which is arranged to slide along the piston tube upon the application of fluid pressure (from compressed air) . The piston tube includes a slot through which a projection of the piston extends. The piston projection is arranged to engage the torpedo such that, when the piston slides along the piston tube, the piston projection pushes the torpedo out of the torpedo tube. However, problems arise with leakage of compressed air from the piston tube, through the slot. Leakage of compressed air reduces the fluid pressure in the piston tube, and thus the force at which the piston is slid along the piston tube. In an attempt to overcome this problem, a tongue seal is provided along the slot. However, providing a perfect seal along the entire length of the slot, whilst still permitting the piston projection to travel along the slot, is virtually impossible.

European Patent No. EP 0295600 B describes a conveyor device for loading and unloading torpedoes in a torpedo tube. The device includes a piston fixed through a piston rod to the torpedo tube, and a cylinder displaceable relative to the piston. A slide, on which a loading platform for an object is attachable, is mounted on the exterior of the cylinder and is driven, during movement of the cylinder relative to the piston, via a cable line. The cable line is located outside the cylinder, has ends securely connected to the torpedo tube, and runs over deflecting rollers in such a way that, during a cylinder stroke, the slide also moves along the cylinder. With this arrangement, the slide covers a greater distance than the cylinder relative to the piston, during a cylinder stroke.

Summary of the Invention

At its most general, the present invention provides: a payload deployment system for a vessel,- such as a submarine, the system comprising an ejection tube and a payload propulsion system, wherein the ejection tube includes an element for ejecting a payload from the ejection tube, the element being connected to the propulsion system, part of which is driven by an electric motor, via a cable attached to part of the propulsion system; and a vessel, e.g. a submarine, including the system.

Thus, according to a first aspect of the invention there may be provided: a payload deployment system for a vessel, the system including: an ejection tube for holding a payload; an ejection element in the ejection tube, the ejection element being moveable in the ejection tube and being arranged releasably to engage the payload; a propulsion system, having an electric motor with a moveable first part; a cable extending between part of the propulsion system and the ejection element; and movement of the first part of the motor of the propulsion system being arranged to cause the ejection element to move in the ejection tube, thereby to eject the payload from the ejection tube.

The cable may be fixed to the ejection element. It may alternatively or additionally be fixed to the ejection tube. In this arrangement part of the cable between the propulsion system and the fixing to the ejection tube engages with the ejection element. This engagement may be in the form of a rotatable pulley.

In the present invention, the cable may be made of wire, synthetic rope (man made) or aramid rope, or could be made from a synthetic or aramid tape.

The propulsion system may be in a number of different forms. For example, it may comprise a cable reeling drum driven by a high torque electric motor. In this instance, the cable would connect the drum to the ejection element.

When, in use, the drum of the reeling system rotates in a manner so as to reel in the cable, the force of the reeling is transmitted through the cable to the ejection element. The cable may be fixed to the ejection element, although such fixing is not essential to achieve the force transmission. As an alternative, for example, the cable may be arranged to pass over a pulley wheel rotatably mounted on the ejection element, with the ends of the cable being e.g. anchored to points on the ejection tube.

Alternatively, the propulsion system may comprise a linear induction motor. In this case, the cable would connect the traveller of the linear induction motor to the ejection element.

The linear induction motor may be of any form, for example one having a planar or tubular stator element.

When, in use, the traveller of the linear induction motor moves, force may be transmitted from the traveller to the ejection element via the cable. The cable may be fixed to the ejection element and fixed to the traveller. In a manner similar to the case of a reeling drum system, such fixing is not essential to achieve the force transmission. As an alternative, for example, the cable may be arranged to pass over a pulley wheel rotatably mounted on the ejection element and/or over a pulley wheel rotatably mounted on the traveller, with the ends of the cable being e.g. anchored to points on the ejection tube/stator. Means of supplying electrical current to the motor may take any form known. When current is supplied to the traveller of the linear induction motor, the traveller experiences a force caused by the magnetic field of ' the stator. This force causes the traveller to move along a path defined by the stator.

In a second aspect of the invention there may be provided a vessel including a payload deployment system of the first aspect. Preferably, the vessel is a submarine. Preferably, the deployment system includes the payload, the payload being located in the payload ejection tube.

The deployment system of the present invention is particularly appropriate for launching a store (e.g. a torpedo) from a submarine (the payload being the store) . The ejection element may releasably engage with the payload prior to movement of the propulsion system, or may releasably engage with the payload only after the propulsion system has begun to move. In the case of the propulsion system comprising a cable reeling drum driven by a high torque electric motor, the drum may be positioned such that it projects into the ejection tube. In the case of the propulsion system comprising a linear induction motor, the longitudinal axis of the ejection tube and the longitudinal axis of the stator of the linear induction motor may be parallel with each other, and the ejection tube and the stator of the linear induction motor may abut one another. This configuration may allow the system to take a compact form.

Preferably, when a current is supplied to the linear induction motor causing the traveller to move, the ejection element moves in an opposite direction to the traveller .

Movement of the ejection element and the traveller in opposite directions may be achieved by running the connecting cable over a cable runner (for example a wheel or a plurality of wheels) . The cable runner may change the direction in which the cable travels (as the cable runs over it) and therefore the direction that forces may be transferred between the traveller and the ejection element . Preferably, the payload ejection tube has an ejection opening at one end, through which the payload may be ejected from the ejection tube, the opening having a releasable cover. The cover may be releasable as a single piece or may be frangible so that breaking of the cover (e.g. upon an impact with the payload) releases it from the ejection opening. The cover may prevent water from entering the ejection tube e.g. if the system of the present invention is employed in a submarine. The ejection element is preferably located at an opposite side of the payload to the ejection opening. Therefore, the ejection element may push the payload toward the ejection opening. If the propulsion system comprises a linear induction motor, the cable may extend from the ejection element, in a first direction, to a first opening in the ejection tube. This may be adjacent the ejection opening. The cable may then travel over a cable runner and connect to the traveller of the linear induction motor, in a second direction which may be opposite the first direction. Thus, when the cable is entrained, the ejection element may apply a pushing force to the payload right up until the moment the payload is fully ejected from the ejection tube. This increases the speed at which the payload may be ejected from the ejection tube. When the cable is fixed to the ejection element and the traveller, the ratio of the speed of movement of the traveller and the ejection element may be 1:1. In the case where the propulsion system comprises a cable reeling drum, the cable may extend from the drum to the ejection element, similarly allowing the payload to be propelled until it is ejected from the ejection tube.

As mentioned, however, the cable may pass over a pulley wheel mounted to the ejection element, instead of being fixed to the ejection element. If the propulsion system comprises a cable reeling drum, the cable may extend from the drum over the pulley wheel to a position where it is fixed or anchored e.g. to the ejection tube. If the propulsion system comprises a linear induction motor, the cable may extend from the traveller, over the pulley wheel to e.g. a position adjacent the ejection opening, where it is fixed or anchored. This configuration may allow a 2:1 ratio in the speed of movement of the traveller and ejection element respectively. This increases the force that the ejection element may apply to the payload. Such an increase in force may be necessary for the payload to e.g. break the frangible cover of the ejection opening. To compensate for the resultant reduction in speed of the ejection element, the ejection tube and stator of the linear induction motor may be lengthened or the drum of the cable reeling system altered.

When the cable is undrawn, that is when the payload is not being ejected from the ejection tube, the propulsion system is at rest and a substantial amount of the cable lies within the ejection tube. When, by driving of the propulsion system, the cable is drawn, the proportion of cable inside the ejection tube decreases. In the case of a cable reeling drum propulsion system, excess cabling is wound around the drum. If the propulsion system comprises a linear induction motor, the cable extends to the traveller, which has moved away from its starting position. When the cable is fully drawn, that is when the ejection of the payload is substantially finished, the substantial proportion of the cable lies outside the ejection tube, for example wound around a reeling drum.

As has been mentioned above, the ejection element moves in the ejection tube to eject the payload from the ejection tube. It is preferable that a fluid flow path is provided into the ejection tube to allow fluid, e.g. water, to enter the ejection tube, preferably to the rear of the ejection element and the payload to enable the ejection tube to fill with fluid as the payload is ejected from the ejection tube. There may therefore be an opening in the ejection tube, which opening defines a fluid flow path between the interior and exterior of the ejection tube. It is then possible to use part of the ejection element to block that opening when the ejection element is in its rest position, prior to ejection of the payload. When the ejection element moves to eject the payload, the opening is unblocked and fluid can enter the interior of the ejection tube. Such an arrangement has the advantage that the unblocking of the opening and the ejection of the payload necessarily occur simultaneously. Alternatively or additionally, there may be a gap in the part of the ejection element that engages the ejection tube to define a fluid flow path around the ejection element.

It is desirable that the payload is retained in the ejection tube is prevented from moving except when it is to be ejected. Therefore, a retention system or latch may be provided which may releasably engage the payload. It may be a latch which is moveable between a position in which it engages with the payload and a further position in which it is disengaged from the payload. The engagement of the retention latch may, for example, be with a projection on the payload which passes through the ejection element. Then, fluid or compressed gas may be supplied, for example via a duct, to a release mechanism for the retention latch, which operates a release mechanism of the retention latch to cause the retention latch to move to its disengaged position, and so release the payload for subsequent ejection from the ejection tube. If fluid or compressed gas is supplied via a duct, the retention system is preferably disengaged when the duct contains said fluid or compressed gas.

The retention latch may operate on the basis of linear or rotational movement. In the latter case, the retention latch may, in a first position, engage projections on the payload, and may then rotate to a position in which such projections are free to move through openings in the retention latch, thereby to permit the payload to be ejected. It is possible for the rotating retention latch to be driven by a mechanism other than those using compressed gas or fluid, such as an electric motor.

Such an arrangement may also be used in which the rotation of the retention latch also unblocks openings in the ejection tube, to permit fluid to enter therein. Instead of blocking those openings using part of the ejection element, as described above, the retention latch may have projections thereon which, when the retention latch is in the engage position, block openings in the ejection tube, which openings are unblocked when the retention latch moves to its disengaged position, thereby permitting fluid, such as water, to enter the ejection tube. Again, because the unblocking of the openings is necessarily simultaneous with the release of the payload from engagement with the retention latch, the fluid can enter the ejection tube only when the payload is to be ejection from the ejection tube.

Alternatively or additionally, the ejection element may be releasably fixed to the walls of the ejection tube by frangible blocks .

Brief Description of the Drawings

Embodiments of the present invention will now be described with reference to the following drawings in which:

Fig. 1 is a cross-sectional side view of a payload deployment system according to a first embodiment of the present invention;

Fig. 2 is a cross-sectional side view of a payload deployment system according to a second embodiment of the present invention;

Fig. 3 is a cross-sectional side view of a payload deployment system according to a third embodiment of the present invention; Figs. 4a to 4e are cross-sectional views of a payload deployment system according to a fourth embodiment of the present invention, at different stages of the ejection of a payload; Fig. 5 is a front view of the payload deployment system of Figs. 4a to 4e;

Fig. 6 is a front view of an ejection element used in the fourth embodiment;

Fig. 7 illustrates a modified release mechanism for use in the fourth embodiment, that release mechanism being in an engaged position; and

Fig. 8 shows the release mechanism or Fig. 7, but in the disengaged position.

Detailed Description

Fig. 1 shows a first embodiment of a torpedo deployment system for a submarine in accordance with the present invention. A torpedo 1 is located within an ejection tube 2. The ejection tube 2 has an ejection opening 21 at one end, through which the torpedo 1 may be ejected from the ejection tube 2. The ejection opening 21 is covered by a frangible cap 22. The torpedo 1 is held in a central position in the ejection tube 2 by guide members 23. The guide members 23 maintain spaces 24 between the torpedo 1 and the walls of the ejection tube 2 and also keep the ends of the ejection tube 2 apart.

A slidable ejection element 25 is located at an opposite end of the ejection tube to the ejection opening 21. The ejection element 25 is slidable towards the ejection opening 21 along substantially the entire length of the tube. The ejection element 25 has a profile that conforms with the internal walls of the ejection tube 2. However, so that the guides 23 do not obstruct sliding of the ejection element 25, the ejection element 25 has corresponding cut-out portions (not shown) . The ejection element 25 has an engagement surface 26 for releasably engaging the torpedo 1. As shown in Fig. 1, the engagement surface 26 releasably engages the rear end of the torpedo 1. Thus, when, in use, the ejection element

25 slides along the ejection tube 2, the torpedo 1 is forced (pushed) out of the ejection tube 2 by the ejection element 25. A projection system is provided to slide the ejection element 25 in the ejection tube 2. The projection system comprises a linear induction motor 37 having a traveller 31 located on a planar stator 3, the traveller being connected to the ejection element 25 by a cable 32.

The stator 3 is of a similar length to the ejection tube 2, and is mounted to one side of the ejection tube 2. The axes of the ejection tube 2 and the stator 3 are parallel .

The stator 3 has a first end 33 and a second end 34.

The traveller 31 is arranged to move toward the second end 34 upon the application of electrical current. To enable this, the stator 3 is magnetic, and the traveller is connected to an electrical power supply (not shown) .

On application of a current to the traveller it moves from the first end 33 of the stator 3 towards the second end 34 of the stator 3. A cable runner 35 (essentially a wheel) is located at the first end 33 of the stator 3. The wheel projects into the interior of the ejection tube 2 via an opening

27 of the ejection tube 2.

The cable 32 runs from the traveller 31, over the cable runner 35 and then through the interior of the ejection tube 2 (in right to left direction as shown in

Fig. 1), to the ejection element 25. The cable 32 runs through the ejection tube 2 in one of the spaces 24 between the torpedo 1 and the walls of the ejection tube 2.

When the traveller 31 slides in a direction from right to left, as shown in Fig. 1, the ejection element 25 is caused to slide in the opposite direction, i.e. from left to right, as shown in Fig. 1, due to a pulling force applied to the ejection element 25 by the cable 32. This causes the ejection element 25 to push the torpedo 1 toward the ejection opening 21, whereupon the torpedo 1 applies force to the frangible cap 22, causing it to break. By breaking, the frangible cap 22 no longer obstructs the opening 21, and ejection of the torpedo 1 from the ejection tube 2 may therefore take place. The frangible cap 22 is weighted so that it falls to the seabed upon breaking.

To prevent the ejection element 25 sliding unintentionally, e.g. as a result of movement of the submarine, the ejection element 25 is releasably fixed to the walls of the ejection tube 2 via frangible blocks 28. Unintentional sliding of the ejection element 25 might damage the torpedo 1 or might even cause the torpedo 1 to be ejected from the ejection tube 2 when this is not desired. Movement of the traveller 31 upon application of electrical current applies sufficient force to the ejection element 25 for the frangible blocks 28 to break, allowing the ejection element 25 to eject the torpedo 1 when desired.

Fig. 2 shows a second embodiment of a torpedo deployment system for a submarine in accordance with the present invention. Features of this second embodiment that are the same as features in the first embodiment have been given the same reference numerals and are not described again. The system of the second embodiment is almost identical to the system of the first embodiment, except for the nature of the stator element 3 of the linear induction motor 37 which drives the traveller 31.

In the second embodiment, the stator 3 has a tubular construction as opposed to the planar construction shown in Fig. 1.

Fig. 3 shows a third embodiment of a torpedo deployment system for a submarine in accordance with the present invention. Features of this third embodiment that are the same as features in the first embodiment have been given the same reference numerals and are not described again. The system of the third embodiment is almost identical to the system of the first embodiment, except that the electric motor driven torpedo propulsion system is a cable reeling drum 36. This drum 36 is driven by a high torque electrical motor (not shown) . The drum 36 protrudes into the ejection tube 2 through a gap 27, allowing a travel path for the cable 32 to run through one of the gaps 24 between the torpedo 1 and the ejection tube 2.

When the high torque electric motor (not shown) is activated the cable reeling drum 36 turns in a manner to reel in the cable 32 which is connected to the ejection element 25. In Fig. 3, this would correspond to clockwise rotation of the drum 36. By reeling the cable 32 in this way, the ejection element 25 will break free of blocks 28 to propel the torpedo 1 towards the opening 21, launching the torpedo 1.

Fig. 4a also shows that between the front of the torpedo 1 and the end cap 322 is a spring shock absorber 62. Moreover, front cap 322 is connected by a frangible seal 64 to the walls of the ejection tube 2.

In order to launch the torpedo 1 from the ejection tube 2, the first stage is that the release mechanism is primed. As shown in Fig. 4b, a valve (not shown) is activated to cause pressurised fluid to pass through the duct 56 to the release mechanism 54, thereby releasing the retention latch 52 from the connector 66, which connector 66 is connected to the end of the torpedo 1. At this stage, the opening 58 is still sealed by the ejection element 350.

In the next stage, illustrated in Fig. 4c, a high torque electric motor (not shown) begins rotation of the reeling drum 36, in a clockwise direction in Fig. 4c.

This draws cable 32 in a left to right direction in Fig. 4c. The action of the cable 32 then moves the ejection element 350 to the right in Fig. 4c. This movement means that the opening 58 is no longer sealed by the ejection element 350 and water passes through that opening 58 into the hollow interior 68 of the ejection element 350, behind the torpedo 1. Note that, at this stage, the cap 322 is still in place, and the frangible seal 64 still intact . However, as the reeling drum 36, cable 32, ejection element 350 and torpedo 1 continue to move, the frangible seal 64 is broken and the cap 322 is expelled from the opening 22 of the ejection tube 2. Thus, the position shown in Fig. 4d is reached. Water continues to enter via the opening 58, flooding the space 70 created within the ejection tube 2 behind the ejection element 350. Note that the ejection element 350 is still engaged with the torpedo 1, because of the force due to the cable 32, and also because of engagement between the ejection element 350 and the connector 66. The water fills the volume behind the torpedo to ensure that pressure effects do not impede the launching of the torpedo. Note also that the cap 322 may be weighted so that it falls clear of the ejection tube 2 once the frangible seal 64 breaks. Finally, the stage shown in Fig. 4e is reached. The torpedo 1 has passed from the ejection tube 2 and is released. The ejection element 350 contacts flanges 72 around the opening 22 and so is held within the ejection tube 2. Substantially the whole of the space 70 corresponding to the interior of the ejection tube 2 is now filled with water.

Fig. 5 shows a cross-sectional view of the arrangement of Figs. 4a to 4e, illustrating how the guide members 23 are arranged around the torpedo 1. Fig. 6 shows an end view of ejection element 350 illustrating the opening 74 into which the connector 66 is received, and also shows that the ejection element 350 may have projections 76 thereon which will engage with the flanges 72. Note that the projections 76 have the effect of creating a flowpath for water around the ejection element. Thus, in the position in Fig. 4d, for example, water may pass from the space 70 around the ejection element 350 as shown by arrow 78 into the space 80 within the ejection tube 2 around the torpedo 1. Thus, again, pressure may be equalised.

In the fourth embodiment discussed with reference to Figs. 4 to 6, the torpedo 1 is held by the retention latch 52, except when the torpedo 1 is to be ejected from the ejection tube 2. The retention latch illustrated in Figs. 4a to 4e has arms which engage the connector 66, the ends of which arms move outwardly to release that connector 66. However, it is possible for the retention latch to operate on the basis of rotation. Thus, Fig. 7 illustrates an alternative configuration of the retention latch, in which that latch is in the form of a disk 80 with an opening 81 therein through which passes the connector 66. In this arrangement, the retention latch 80 has projections 82 which extend inwardly in the opening 80, and in the retention position shown in Fig. 7, engage projections 83 on the connector 66. Thus, the torpedo 1 is held in the ejection tube 2. When the torpedo 1 is to be released, the retention latch 80 rotates about axis 84 to the position shown in Fig. 8 in which the projections 83 on the connector 66 are aligned with the gaps between the projections 82. Thus, the connector 66 is disengaged from the retention latch 80, and hence the torpedo 1 is free to move in the ejection tube 2.

The rotation of the retention latch 80 may be driven by compressed gas or fluid, as in the arrangements illustrated in Figs. 4a to 4e.

Figs. 7 and 8 illustrate another modification of the third embodiment. In the arrangements illustrated in Figs. 4a to 4e, the opening 58 is blocked by the ejection element 350 until that ejection element 350 moves as part of the operation of ejecting the torpedo 1. In the arrangements shown in Figs. 7 and 8, there are openings 85 in the ejection tube 2, and the release latch 80 has outwardly extending projections 86. When the ejection element 80 is in the engaged position, illustrated in Fig. 7, those outwardly extending projections 86 block the openings 85. However, as can be seen from Fig. 8, when the retention latch 80 rotates to release the connector 66, the outwardly extending projections 86 move to a position where they are clear of the openings 85, thus permitting fluid to enter through those openings 85 into the ejection tube 2.

Claims

Claims :

1. A payload deployment system for a marine vessel, the system including: an ejection tube (2) for holding a payload (1); an ejection element (25) in the ejection tube (2), the ejection element (25) being moveable in the ejection tube (2) and being arranged releasably to engage the payload (1) ; a propulsion system (36, 37) for moving the ejection element (25), the propulsion system having an electric motor with a moveable first part; and a cable (32) extending between the propulsion system (36, 37) and the ejection element (25), wherein movement of said first part is arranged to cause movement of the cable (32) which causes movement of the ejection element (25) in the ejection tube (2), thereby to eject the payload (1) from the ejection tube (2) .

2. A payload deployment system according to claim 1, wherein movement of the cable (32) at a speed relative to the propulsion system (36, 37) is arranged to cause movement of the ejection element (25) relative to the ejection tube (2) at that speed.

3. A payload deployment system according to claim 1 or claim 2, wherein the cable (32) is fixed to the ejection element (25) .

4. A payload deployment system according to any one of claims 1 to 3, wherein the cable (32) is fixed to the ejection tube (2) and part of the cable (32) between the propulsion system (36, 37) and the fixing to the ejection tube (2) engages with the ejection element (25) .

5. A payload deployment system according to claim 4, wherein the engagement with the ejection element (25) is via a pulley rotatably mounted on the ejection element (25) .

6. A payload deployment system according to any one of the preceding claims, wherein the first part of the motor of the propulsion system is a drum reel (36) adapted to reel the cable (32), the cable (32) being attached to the drum (36) , the drum being rotatable when the motor is driven.

7. A payload deployment system according to any one of the preceding claims, wherein the propulsion system comprises a linear induction motor (37), the motor having a moveable traveller element (31) forming said first part of the motor of the propulsion system and a stator element (3) along which the traveller element can travel.

8. A payload deployment system according to claim 7, wherein the stator (3) of the linear induction motor (37) is of a planar form.

9. A payload deployment system according to claim 7, wherein the stator (3) of the linear induction motor (37) is of a tubular form.

10. A payload deployment system according to any one of claims 7 to 9, including a first opening (27) in the ejection tube (2), wherein the cable (32) passes through the first opening (27) .

11. A payload deployment system according to claim 10, including a cable runner (35) located in or adjacent to the first opening (27), wherein the cable (32) passes around the cable runner (35) such that the path of the cable (32) is changed by the cable runner (35), the path of the cable (32) from the ejection element (25) to the first opening (27) in the ejection tube (2) being in a different direction from the path of the cable (32) from the cable runner (35) to the traveller (31) of the linear induction motor (37) .

12. A payload deployment system according to claim 11, wherein the cable runner (35) is a pulley wheel.

13. A payload deployment system according to any one of the preceding claims, wherein a part of the ejection element (25) engages the ejection tube (2) and said part has at least one gap therein thereby to define a fluid flow path around the ejection element (25) in the ejection tube (2) .

14. A payload deployment system according to any one of the preceding claims, wherein: the ejection element (25) is moveable in the ejection tube (2) between a rest position, at which the cable (32) is undrawn, and a deployed position, at which the cable (32) is fully drawn; the ejection tube (2) includes a second opening (58) in the longitudinal surface thereof, which second opening (58) defines a fluid flow path between the interior and the exterior of the ejection tube (2); and the second opening (58) is blocked by an external surface of the ejection element (35) when the ejection element (35) is in the rest position, and is unblocked when the ejection element (35) is in the deployed position .

15. A payload deployment system according to any one of the preceding claims, wherein the ejection tube (2) includes a payload retention system (54) having a retention latch (52, 80) arranged to releasably engage with the payload (1) .

16. A payload deployment system according to claim 13, wherein the retention latch (80) is rotatable between a first position at which it is engaged with the payload

(1) and a second position at which it is disengaged from the payload (1), and means for driving the retention latch (80) to rotate it from the first position to the second position.

17. A payload deployment system according to claim 15 or claim 16, wherein the payload retention system comprises a release mechanism (54) connected to the retention latch (52) and a means for supplying compressed gas or fluid to the release mechanism (54), the release mechanism (54) being arranged to disengage the payload from the retention latch (52) when it is supplied with compressed gas or fluid by the means for supplying compressed gas or fluid.

18. A payload deployment system according to claim 17, including a duct (56) arranged to transfer compressed gas or fluid from the means for supplying compressed gas or fluid to the release mechanism (54) .

19. A payload deployment system according to any one of the preceding claims, wherein the ejection element (25) is releasably fixed to the ejection tube (2) via frangible blocks (28) .

20. A marine vessel including a payload deployment system of any one of claims 1 to 19.

21. A marine vessel according to claim 20, wherein said marine vessel is a submarine.