Abstract:
A retrofitable breech is disclosed for use on existing tubes for launching vehicles, such as torpedoes. The breech utilizes gas generators such as commercial off the shelf automotive airbag inflators, for propelling the torpedo from the tube. A plurality, typically three or four, generators are used and are fired in sequence with a controlled time delay. A retrofitable device is also disclosed for activating the weapons securing mechanism to release the torpedo. In addition, a release mechanism is disclosed for pulling the electrical connector plug on the torpedo. The sequence of releasing the torpedo, retraction of the plug and firing the inflators is controlled by a controller upon initiation of the firing sequence.

Description:
The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms, as provided for by the terms of contract No. N66604-97-C-2332 awarded by the Naval Undersea Warfare Center. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to torpedo tubes for surface ships, and more particularly to an improved torpedo tube breech therefor and a method for launching torpedoes. 
     BACKGROUND OF THE INVENTION 
     The vast majority of surface ships worldwide utilize substantially the same mechanism and method for launching lightweight vehicles, such as torpedoes, from a tube. This technology was first developed in the 1950&#39;s, and has been utilized virtually unchanged since that time. 
     A conventional tube used for launching a lightweight vehicle, such as a torpedo, from a surface ship is schematically illustrated in FIGS. 1 and 2. In existing systems, the torpedoes are carried in a tube  10  disposed on the surface of the ship. Tube  10  is generally cylindrical in shape, and includes a discharge end  12  having a closure  16  and a breech end  14 . A torpedo  18  with fins  13  is manually loaded into tube  10  through discharge end  12 , upon opening of closure  16 . Torpedo  18  resides in closely spaced relation with ridges or lands  15  on the side walls of tube  10 . Ridges  15  are raised areas on the interior surface of the tube  10  which extend parallel to the long axis of the tube. Ridges  15  are designed not only to guide the fins  13  of the torpedo  18  but also to allow the body of the torpedo to fit snugly within the tube while allowing free passage of the fins  13 . Ridges  15  also contribute to a pressure buildup upon launch, as they restrict the space within which the gas may escape in a forward direction. 
     Breech end  14  includes breech  20 , and a weapons securing mechanism  24  for retaining the torpedo  18  within tube  10  during storage. Breech  20  is affixed to tube  10  by locking ring assembly  115 , which comprises an interrupted screw mechanism. Rotation of locking ring assembly  115  allows opening of breech  20  and loading of a vehicle, such as a torpedo  18 , into the breech end  14 . Breech  20  includes a flask  22  and a control mechanism  26  responsive to a firing command for releasing the torpedo and expelling it from tube  10 . Flask  22  contains air under high pressure. An air port  28  couples the interior of flask  22  to control system  26 . Firing valve  30  permits air from within flask  22  to escape into tube  10  to expel torpedo  18 , once valve  30  is opened. Weapons securing mechanism  24  includes jaws  32  which are configured to grasp a correspondingly shaped end tip  19  of the torpedo  18 . Jaws  32  retain torpedo  18  in its desired position within tube  10  under normal, non-firing conditions. Jaws  32  are disposed within cylinder  31  which is slidably mounted. Cylinder  31  holds jaws  32  in their closed position grasping tip  19 . Pressurized gas passed to port  27  from air port  28  by way of control system  26  causes cylinder  31  to move away from flask  22  (to the left as shown in FIG. 2) allowing the jaws  32  to open as the outer surfaces of the jaws  32  ride along sloped surface  33  of cylinder  31 . Movement of cylinder  31  toward flask  22  closes jaws  32 . 
     Firing valve  30  includes closure  34 , sliding portion  36  and spring  38 . Spring  38  biases sliding portion  36  against closure  34  into a normally closed position to prevent air within flask  22  from escaping to the interior of tube  10  under normal, non-firing conditions. A lever  40  is pivotally coupled to cylinder  31  at point  41 , so that when cylinder  31  moves away from flask  22 , lever  40  pivots and presses sliding portion  36  toward flask  22  and against the bias of spring  38  to unseat valve  30  and to allow air to escape into tube  10 . 
     Tube  10  also includes an electrical connection  50  which provides electrical signals and power to torpedo  18  when it is being stored within tube  10 . Electrical connection  50  includes an umbilical cable  52  and a plug  54  which is normally coupled to a correspondingly shaped female receptacle (not shown) in torpedo  18 . Umbilical cable  52  is coupled to a lever arm  56  which is in turn coupled to a valve  58 . When pneumatically actuated by air from control system  26 , valve  58  pivots lever arm  56  to retract plug  54  from torpedo  18 . 
     In operation, closure mechanism  16  is first opened to allow the torpedo  18  to pass through discharge end  12 . When a command is received by control system  26  to fire the torpedo, air is bled through port  28  from the interior of flask  22  into control system  26  via a valving mechanism (not shown). The air from port  28  is conducted to port  58  to cause pivoting of lever arm  56  and thus retraction of plug  54 . The air is then conducted through port  27  to cylinder  31  of weapons securing mechanism  24  causing jaws  32  to open, and lever  40  to pivot about pivot point  41 . Lever  40  depresses sliding portion  36 , opening firing valve  30  and releasing the high-pressure air from within flask  22  into the interior of tube  10 . This air pressure is calculated to be sufficient to expel torpedo  18  from tube  10  once jaws  32  are opened to release end tip  19 . 
     The structure and operation of the foregoing prior art torpedo tube and launching mechanism are fully described in Technical Manual SW395-AC-MMO-010/OP3355, NSNO640-LP-002-3000 entitled  Description, Operation, Maintenance, and Illustrated Parts Breakdown, Surface Vessel Torpedo Tube Mark  32  Mods  5  and  7, which is published by direction of the Commander, Naval Sea Systems Command. The latest revision of this technical manual is dated Sep. 16, 1988, and is specifically incorporated herein by reference. 
     This prior art system has several drawbacks. In the first place, after a torpedo is manually loaded into tube  10  through breech end  14  after opening of breech  20 , breech  20  must be recharged with high-pressure air. About 1600 lbs of air pressure are required for each flask  22 . Therefore, it takes about one to one and one half hours to recharge the flasks for all six tubes that are normally carried on a typical ship. In adverse weather, the time required to recharge the flask in each tube can be potentially much longer. For those ships having tubes in external location outside the skin of the ship, the charging operation is also very hazardous if it must be performed in bad weather or in the dark. Some ship classes necessitate training the tubes outboard prior to charging. This recharge time produces a lengthy delay between the firing of one round of torpedoes, and readiness to fire the next round of torpedoes. Such a delay could prove disastrous in a combat situation. 
     Another drawback of the existing system is that all of the flasks presently found on most ships in the fleet have corrosion problems. As a partial consequence of these corrosion problems, the flasks do not hold the air charge indefinitely. They have to be recharged regularly, typically every 12-24 hours. Therefore, combat readiness could be affected by the failure to ensure that each flask remains fully charged. 
     Another problem associated with existing systems is that misalignment of the breech with respect to weapons securing mechanism  24  could and has caused accidental movement of lever  40  and opening of flask  22 . Such an accidental opening could cause the breech to fly off while assembling the breech, or while charging the flask. Obviously, such a condition can be quite dangerous to the crew members who are involved in manually loading the tube and charging the flasks. Serious accidents have occurred during the removal and reinstallation of the air flasks, resulting in personal injury and loss of valuable man days, not to mention loss of combat readiness. 
     Also, all of the pneumatics associated with each tube are exposed to the salt atmosphere, and are subject to corrosion problems requiring frequent and intensive maintenance and repair. 
     SUMMARY OF THE INVENTION 
     The foregoing drawbacks of existing vehicle launch mechanisms for surface ships are overcome by the present invention, in which the air flasks in existing breeches are replaced by gas generators, which, in a preferred embodiment, are commercially available, automotive air bag gas generator inflators, that provide the energy needed to launch a vehicle, such as a torpedo, from a tube. 
     In one aspect of the invention, a new breech assembly is retrofitted on the breech end of an existing tube. This new breech is constructed with a retaining device containing a plurality of gas generators which are replaceable after use. This new breech assembly is retrofitted onto the existing locking ring assembly on the breech end of the tube. The retaining device provides adequate support for the gas generators to retain them in place during activation and allows rapid replacement of the gas generators after use. 
     In another aspect of the invention, a plurality of gas generators are employed and are activated sequentially with a predetermined time delay. This predetermined time delay produces a pressure wave of predetermined and predictable characteristics which expels the vehicle with the desired velocity and acceleration. By adjusting the number and sequence of the gas generators, the pressure wave developed by the prior art air flask can be easily replicated. This sequential firing of the gas generators preferably is electrically controlled. 
     In another further aspect of this invention, a cartridge is disclosed for activating the weapons securing mechanism to release the tip end of the vehicle, such as a torpedo, prior to launch. This cartridge is typically a small explosive device that can be retrofitted into the existing weapons securing mechanism pressure line to create the necessary gas pressure to open the jaws of the weapons securing mechanism. 
     In yet another further aspect of the invention, an improved umbilical release mechanism is disclosed for pulling the umbilical cable prior to launch. This improved umbilical release mechanism preferably is an electrically or pneumatically operated piston which pulls the existing umbilical cable in response to the launch signal. 
     By eliminating the need to use high-pressure air to launch a vehicle, such as a torpedo, this invention eliminates the time-consuming requirement of recharging the air flask following a launch. All that is required is replacement of the gas generators in the breech after loading of the vehicle, which can be accomplished in a relatively small amount of time. Since automotive air bag gas generators have been available for some time for automotive use, have a shelf life of 20 years, and have been demonstrated to be essentially leakproof, the risks of leaks are virtually non-existent. Thus, this invention also eliminates the need to continually recharge the flasks each 12-24 hours. Moreover, the leakage of air due to corrosion has been eliminated, and the risk of the breech flying off has also been eliminated, since high-pressure gasses are no longer used for the control mechanism. 
     As a consequence, the potential for injury is virtually eliminated. The tubes are always combat ready once the gas generators have been loaded, and the time required to render a particular tube firing ready after launch is substantially reduced. As a result, the ship can be maintained in a higher state of combat readiness than is possible with existing systems. Also, significantly less maintenance is required to maintain this combat readiness. 
     Finally, significantly, the implementation of this mechanism does not require replacement of existing tubes or changes in the method of loading or firing existing torpedoes. Rather, this improved breech mechanism can be retrofitted onto existing tubes utilizing the existing locking flange design and firing electronics. As a result, all existing hardware can still be used, including storage racks, handling equipment and launch computers. Also, most operational procedures can be maintained, or even eliminated as the reloading process is streamlined. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be more fully appreciated from the following detailed description, when taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a perspective, schematic view of a conventional vehicle launch tube; 
     FIG. 2 is a partial, cross-sectional, side schematic view of the tube of FIG. 1 illustrating the firing mechanism; 
     FIG. 3 is a cross-sectional side view of a tube in accordance with the present invention, illustrating the position of the vehicle prior to firing; 
     FIG. 4 is a partial, cross-sectional side view of the tube and vehicle of FIG. 3; 
     FIG. 5 is a perspective view of the breech plate and locking flange of the tube of FIG. 3; 
     FIG. 6 is a perspective view of the breech plate of FIG. 5 illustrating insertion of the gas generators; 
     FIG. 7 is a perspective view of the breech cover and locking flange of the tube of FIG. 3; 
     FIG. 8 is a perspective view of the weapon securing mechanism of the tube of FIG. 3; 
     FIG. 9 is a partial, cross-sectional view of the tube of FIG. 3 illustrating the vehicle exiting the tube after firing; 
     FIG. 10 is a partial, cross-sectional side view of the tube and vehicle of FIG. 3 illustrating another embodiment of this invention; and 
     FIG. 11 is a cross-sectional view of the breach end of the tube of FIG. 3 taken along the line  11 — 11  of FIG.  9 . 
     FIGS. 12-15 are tables and charts related to certain parameters and the performance of the current invention. 
    
    
     DETAILED DESCRIPTION 
     With reference now to the drawings, and more particularly to FIGS. 3 and 4 thereof, an exemplary embodiment of one aspect of the present invention will be described. Like numbers will be used for those elements of the novel launch mechanism which are identical or similar to those elements of existing, conventional launch mechanisms as illustrated in FIGS. 1 and 2. 
     FIG. 3 illustrates a vehicle disposed within tube  10 . The vehicle typically is a torpedo  18  which has fins  13  riding between ridges  15  without contacting ridges  15 . Tube  10  of FIGS. 3 and 4 is identical to tube  10  of FIGS. 1 and 2, except for the breech end, which will be described hereinafter. As shown in FIG. 3, end tip  19  of torpedo  18  resides within jaws  32  of weapons securing mechanism  24 . 
     Novel breech assembly  100  of this invention includes breech plate  102 , retaining device  104  mounted on breech plate  102 , gas generators  106  disposed within retaining device  104 , breech cover  108 , locking flange  110  and controller  134 . 
     Breech plate  102  and locking flange  110  will now be described in more detail with particular reference to FIGS. 5,  6  and  11 . Breech plate  102  is affixed by fixation devices  112  such as bolts, rivets or other suitable devices, to a locking flange  110 . Locking flange  110  is similar to a locking flange used to mount breech  20  to tube  10  of a conventional system, as shown in FIGS. 1 and 2. Locking flange  110  includes raised, spaced locking elements  114  positioned at fixed intervals around the circumference of flange  110 . These locking elements  114  form an interrupted screw when mated with a conventional rotatable locking ring assembly  115  on the breech end  14  of a torpedo tube  10 . Locking ring assembly  115  contains mating, raised, spaced locking elements  117  disposed on an interior surface. When breech plate  102  and locking flange  110  are mounted onto the breech end  14  of tube  10 , locking flange  110  is guided into the proper alignment by key  119  riding in a keyway (not shown), so that the spaces between locking elements  114  are aligned with but behind locking elements  117  on locking ring assembly  115 . Thereafter, locking ring assembly  115  is rotated in a counterclockwise direction, as shown in FIG. 5, about the central axis of tube  10  approximately 22.5 degrees into a locked position in which the corresponding locking elements  117  of assembly  115  are aligned with elements  114  on the locking flange  110 , and in which elements  117  are disposed on a side of elements  114  facing the inside of tube  10  to lock breech plate  102  and locking flange  110  on breech end  14 . Locking ring grip handle  121  contains ball detents (not shown) which tell the operator when locking ring assembly  115  is in the locked or unlocked position and retain assembly  115  in a locked or unlocked position. Latch and bracket assembly  123  on handle  121  is clamped to assembly  115  to prevent rotation of ring assembly  115  from its locked position. The foregoing steps are reversed to remove flange  110  and breech plate  102  from tube  10 . A handle  116  is provided on locking flange  110  to permit easy manual removal and replacement of the combination of locking flange  110  and breech plate  102 . 
     Breech plate  102  has mounted on it, or incorporated into its structure, retaining devices  104 . Retaining devices  104  include tubes  105  configured to accept gas generators  106  ( 106 ( a ),  106 ( b ),  106 ( c ) and  106 ( d )) and their associated cables  136 . Devices  104  are sufficiently sturdy, and are mounted to breech plate  102  in a sufficiently sturdy manner to allow devices  104  to sustain the high pressures generated by gas generators  106  and to direct all of the thrust forward into the interior of tube  10 . Each tube  105  of each retaining device  104  is provided with a cover  118  which is threadably mounted, or mounted in some other suitable manner, on an opening  120  of tube  105 . Cables  136  of gas generators  106  extend through openings in covers  118 . For purposes of illustration only, breech plate  102  is illustrated as having two retaining devices  104  with four tubes  105 . However, it is to be understood, that a smaller or greater number of retaining devices  104  and tubes  105  could be used, depending upon the launch requirements of a particular vehicle. 
     Gas generators  106  typically are inserted or replaced through opening  120 . However, gas generators  106  could be inserted into tubes  105  from the other side of breech plate  102  through opening  124 . The joint between device  104  and opening  124  is sealed with an O-ring or other like seal  126  to render the joint gas tight. Gas generators  106  each preferably have an enlarged lip  107  adjacent cover  118 . Lip  107  together with a very snug fit of gas generators  106  within tubes  105  seal the opening in cover  118  for cables  136  and prevent any leakage of gases through cover  118 . 
     Breech plate  102  also includes opening  128  through which cable transit  130  extends in a gas tight relationship. Cable transit  130  permits electrical control cables  132  to extend therethrough. An acceptable cable transit  130  can be purchased commercially from Nelson Firestops under model no. RGS-2 Also mounted onto the breech plate  102  is a controller  134  which controls the firing sequence of gas generators  106  and other aspects of the tube  10 . Controller  134  is coupled to each gas generator  106  by its cable  136 , and is coupled to weapons securing mechanism  24  and release mechanism  150  by cables  132 . Controller  134  preferably is hard-wired, but could also be programmable. 
     Breech cover  108  covers breech plate  102  and all of the foregoing elements mounted thereon. Breech cover  108  seals the breech end of tube  10 . As illustrated in FIG. 7, breech cover  108  is secured to breech plate  102  by bolts, rivets, quick release mechanisms, or other suitable mechanisms  138 . Mechanisms  138  permit removal of breech cover  108  to allow ready access to devices  104  and breech plate  102 . 
     Weapons securing mechanism  24  will now be described with particular reference to FIGS. 8 and 11. Weapons securing mechanism  24  of the present invention is substantially identical to that found in existing tubes  10 , and includes jaws  32  which are configured to engage and restrain tip  19  of torpedo  18 , a handle  140  to allow for easy manual replacement and mounting plates  144 . Tube  10  includes mounting brackets  145  disposed on opposed interior walls. Mounting plates  144  of weapons securing mechanism  24  are insertable into brackets  145 , as shown in FIG. 11, and include pins  143  which are slidably disposed within plates  144 . Pins  143  are configured and structured to extend into correspondingly formed openings in bracket  145  to retain weapons securing mechanism  24  within brackets  145 . Handle  140  is pivotally secured to mounting plates  144  at pivots  147  which permit handle  140  to be pivoted approximately 180 degrees, from the position shown in FIG. 11 or in an upwardly facing direction, to a position facing downwardly in FIG. 11 toward the bottom of tube  10 . Pins  149  coupled to handle  140  at pivots  147  engage pins  143  in a known manner, such as through a conventional camming or gearing mechanism to move pins  143  upwardly into the openings in bracket  145  or downwardly to withdraw pins  143  from the openings, in response to pivoting of handle  140 . As shown in FIG. 11 with handle  140  facing in an upward direction, pins  143  have been moved upwardly to extend into corresponding openings formed in brackets  145  to lock mechanism  24  into brackets  145 . When handle  140  is pivoted in a downwardly direction, as shown by the arrow in FIG. 11, pins  143  are moved downwardly to be withdrawn from the openings in brackets  145  to permit removal of mechanism  24 . When mechanism  24  is inserted into tube  10 , it is inserted into brackets  145  from the breech end  14  with handle  140  pointing downwardly. Thereafter, handle  140  is manually raised to lock mechanism  24  into place. Handle  140  also permits manual grasping and deployment of mechanism  24 . 
     The weapons securing mechanism  24  of the present invention does not include firing valve  30  of the prior art. In the present invention, in one embodiment, port  27  of weapons securing mechanism  24  is coupled to an initiator  142 , rather than to the control system  26  of the prior art. Initiator  142  is in turn electrically coupled to controller  134  by cables  132 . Actuation of initiator  142  generates a gas under pressure which is coupled to port  27  by direct physical connection of initiator  142  to port  27 . The gas emitted from initiator  142  causes jaws  32  to open in the same manner that gas received from control system  26  caused jaws  32  to open in a conventional launch mechanism. Initiator  142  must be replaced after each firing of a torpedo  18 . 
     Initiator  142  preferably develops a force of about 1600 psi±200psi in a 16 cm 3  volume. This pressure is sufficient to activate jaws  32 . Any type of device that develops such a gas pressure will suffice for initiator  142 , so long as it can be readily activated and so long as no toxic fumes are released. Typically, initiator  142  may be a small cartridge which contains an explosive device. A preferred initiator  142  is the firing device used on missiles, particularly a Tomahawk missile. This device can be purchased from Special Devices, Inc., 16830 West Placerita Canyon Road, Newhall, Calif. 91321 under part number 103377-32. 
     In an alternative embodiment, as illustrated in FIG. 10, a separate gas generating device  155  is mounted in breech plate  102  and is fluidly coupled to port  27  by a hose  156  or the like. Device  155  may be similar to initiator  142  or it may be a carbon dioxide cartridge, or any other source of pressurized gas. Device  155  would be replaced with gas generators  106  in the same operation, such as by completely removing and breech plate  102  and replacing it with a new breech plate  102  containing fresh gas generators  106  and a device  155 . In a further alternative embodiment, hose  156  could be fluidly coupled to a gas generator  106  so that port  27  is directly coupled to the gas issuing from gas generator  106 . Gases emitted from gas generator  106  activate jaws  32  to open them in the same manner as in the prior art. 
     As in conventional tubes  10 , there is an umbilical cable  52  and associated plug  54  which is normally inserted to a correspondingly-shaped female receptacle (not shown) in torpedo  18 . Cable  52  provides control signals and power to torpedo  18  when stored within tube  10 . Umbilical release mechanism  150  of the present invention preferably includes an electrically actuated cylinder  152 , such as a solenoid. Cylinder  152  could also be pneumatically actuated, or cylinder  152  could be activated by gases received from gas generators  106 . Cylinder  152  is coupled by arm  154  to cable  52 . Actuation of cylinder  152  by controller  134  causes a pulling action on cable  52  to pull plug  54  from the female receptacle in torpedo  18 . 
     As used herein, the term “gas generator” is defined as including any replaceable, self contained, sealed device that generates non-toxic, non-corrosive gases under pressure in a controlled manner either as a by-product of a chemical reaction or through release of a stored compressed gas, or both, in response to an electrical signal. Gas generators  106  preferably are standard, commercial, off-the-shelf automotive air bag inflators, and most preferably, hybrid gas generators. Equally acceptable, newer hybrid gas generators are of the boosted-argon-hybrid type. Pyrotechnic gas generators may also be used. Each automotive hybrid gas generator is a small, high pressure, high reliability flask that contains a quantity of an inert gas, such as Argon, under pressure. On ignition, a small solid propellant such as sodium azide (Arcite) burns and generates a gas which mixes with the Argon in the vessel to heat it. A seal of the pressure vessel containing argon is either burned, burst, or ruptured using a piston. The gas from the propellant is mixed with the argon gas and escapes through a thrust-neutralized port. Roughly one half the energy comes from the solid propellant. A typical hybrid gas generator produces about twenty-five kilojoules of energy. Such hybrid gas generators are readily available and are produced by several vendors, such as Bendix Atlantic Inflator Company (now owned by Atlantic Research Corporation). Typical, acceptable, gas generators and their methods of operation are described in one or more of the following patents, the contents of which are expressly incorporated herein by reference: U.S. Pat. Nos. 3,723,205; 3,756,621; 3,895,821; 5,033,772; 5,076,607; 5,345,876; 5,577,769; 5,589,141; 5,601,310; 5,747,730; 5,763,821; 5,850,053; 5,861,571; and 5,997,666. An acceptable Bendix inflator is sold under the following part number: DOT E-1149413575. Characteristics of such an acceptable inflator are set forth in FIG.  12 . 
     Such automotive hybrid gas generators are extremely desirable because they are each built to standards that are set by the automotive industry and that exceed military standards for reliability. Such generators meet military-like specifications for longevity, impact and insensitivity as munitions. The combustion product which is an argon-gas mix is benign. The firing readiness of such hybrid gas generators does not degrade over time. Shelf life of these generators is at least twenty years with no maintenance or inspection required. 
     As indicated, any number of gas generators  106  may be used in this invention. While four gas generators  106  are shown for purposes of illustration, a smaller or larger number could be used, depending upon the performance desired. Moreover, gas generators  106  could be fired sequentially, simultaneously, or in any combination thereof as is necessary to produce the desired exit velocity and acceleration forces for torpedo  18 . Preferably, the number of gas generators  106  and the time delay between inflator firings are selected to replicate the pressure wave created by the prior art air flask. For most applications of this technology to lightweight torpedoes launched from a surface ship where the torpedo is less than 21 inches in diameter and weighs 450-800 pounds, the minimum velocity upon exit of the torpedo from end  12  of tube  10  is about 33 feet/sec. and the maximum acceleration should not exceed 20 g&#39;s. Typically, to achieve these results, either three or four gas generators are used, and the time delay between firing of the gas generators is about 20 milliseconds, although time delays of 20, 30 and 40 milliseconds have been used. The greater the number of gas generators used, typically the greater the acceleration and exit velocity. The acceleration and exit velocity also can be increased by decreasing the time delay between firings. 
     Test results are set forth in FIG.  13 . As can be sees, test  1  used an unballasted MK50 torpedo weighing 419 lbs. Four gas generators were used, and the time delay was 20 milliseconds. Actual measured exit velocities were about 43.1 feet per second. FIG. 14 discloses in graphic form the acceleration, velocity and position of the torpedo with time for launch  1 . 
     Launch  2  utilized an MK46 torpedo and three gas generators. The time delay for the gas generators was again 20 milliseconds. The exit velocity was measured at somewhere between 33.4 and 35.5 feet per second with the peak acceleration being 18 g&#39;s. FIG. 15 provides in graphic form the internal tube pressure in pounds per square inch versus time generated by the gas generators for a preferred launch profile. 
     Launch  3  was essentially identical to launch  2  in all respects and generated actual exit velocities of about 32.3 feet per second and peak accelerations of about 17 g&#39;s. 
     Launch  4  again used an MK46 torpedo. However, this time four gas generators were used with 20 millisecond delays. The peak exit velocity was between 44.2 and 45.6 feet per second. It was noted that this launch produced the most pressure, temperature and exit velocity on the MK46. However, even with four gas generators, the peak acceleration generated was no higher than that with three gas generators as used in launch  2 . While the peak temperature was measured to be as high as 260° F, no physical damage was noted. 
     Launch  5  utilized an MK50 torpedo with four gas generators and a 20 millisecond delay. The quadrants were shimmed, thus reducing the blow-by area by 2.1 square inches. As a result, the measured exit velocity was between 52 and 52.4 feet per second, much greater than for launch  1  which utilized the same torpedo, but in which the quadrants were not shimmed. 
     Launch  6  was identical to launch  4 , but varied the gas generator ignition intervals to decrease the acceleration on the MK46 torpedo. Time delays of 20, 30 and 40 milliseconds were utilized. Exit velocities ranging between 39.2 and 41.8 feet per second were observed. A peak acceleration of only 12 g&#39;s was generated. 
     Launch  7  used an MK46 torpedo and four gas generators. The time delay between the firings of the first two gas generators was 40 milliseconds, the time delay between the next two gas generators was 30 milliseconds; and the time delay between the last two gas generators was 20 milliseconds. An exit velocity of 37.31 feet/second was observed. 
     Launch  8  used an MK50 torpedo with four gas generators with a constant 20 millisecond time delay. An exit velocity of 31.26 feet/second was observed. Both launches  7  and  8  used an actual exercise torpedo which was fired from a barge in the water and both launches validated the desired water entry angle and speed. 
     The method of operation of the improved breech of this invention will now be described with particular reference to FIGS. 3-9 and with reference to launching of a torpedo. As shown in FIG. 3, prior to launch, torpedo  18  rests in tube  10  and is restrained by jaws  32  of weapons securing mechanism  24 . Plug  54  is inserted into the female receptacle in torpedo  18  which is used for programming the torpedo. Upon commencement of the launch sequence, closure  16  is opened. A signal is sent to controller  134 . Controller  134  in turn sends an electrical signal via cables  132  through cable transit  130  to initiator  142  which is fired to release gases through port  27  moving cylinder  31  to the left as shown in FIG. 2, causing jaws  32  to open. At approximately the same time, an electrical signal is sent to cylinder  152 , which can either be a pneumatically operated cylinder or an electrically operated cylinder, such as a solenoid. Cylinder  152  retracts arm  154  and thus umbilical cable  52  from torpedo  18 . At approximately the same time, controller  134  sends a series of discretely timed signals to sequentially fire gas generators  106 . The delay between the release of jaws  32  and the activation of cylinder  152 , and the firing of the gas generators  106  typically is on the order of milliseconds. The firing sequence has been pre-programmed or hardwired into controller  134 , although in an alternative embodiment, controller  134  could be programmable. Preferably, four gas generators  106  are used, and the gas generators are fired sequentially with a delay of about 20 milliseconds between each one. Typically, although not necessarily, to achieve a balanced generation of pressure within tube  10 , the firing sequence is as follows: generator  106   a,  generator  106   d,  generator  106   b  and generator  106   c.  However, other sequences, arrangements and timing delays could be used as desired to produce the desired exit velocity, acceleration forces and pressure within tube  10 . As gas generators  106  release gases within tube  10 , a back pressure develops behind the midsection of the torpedo. This pressure buildup is due to the relatively tight tolerances between the outer surface of the torpedo  18  and the inner surfaces of tube  10 . The pressure buildup behind the tail of torpedo  18  increases until the torpedo begins to move forward and is ejected at a specific, controllable exit velocity as set forth above in the launch examples. Once out of the tube  10 , torpedo  18  is propelled in a conventional manner which is well-known in the art and will not be further discussed herein. 
     Upon completion of the launch, breech plate  102 , flange  110 , and breech cover  108  are removed as a unit. Breech plate  102  and flange  110  are held stationary by means of handle  116 . Latch and bracket assembly  123  are released and locking ring assembly  115  is rotated about 22.5 degrees in a clockwise direction, as shown in FIG. 11, or until assembly  115  is in its unlocked position in which locking elements  114  are disposed between locking elements  117 . Ball detents on grip handle  121  tell the operator when assembly  115  is in the unlocked position and grab and hold assembly  115  in the unlocked position. Since locking flange  110  is then released, flange  110  and plate  102  may be removed as a unit from breech end  14 . In addition, weapons securing mechanism  24  is released by rotating handle  140  downwardly, as shown in FIG. 11, to retract pins  143  to release plates  144  from brackets  145 . Mechanism  24  is then removed as a unit by manually grasping handle  140  and withdrawing mechanism  24  from brackets  145 . A new torpedo  18  is inserted into tube  10  through breech end  14  and plug  54  is inserted into the female receptacle on torpedo  18 . A new weapons securing mechanism  24  is installed with a fresh initiator  142  mounted therein. Alternatively, mechanism  24  is installed and hose  156  is connected to a device  155  or gas generator  106  mounted on breech plate  102 . A combination of locking flange i  10  and breech plate  102  in which tubes  105  have been supplied with fresh gas generators  106  is installed and is covered by breech cover  108 . Gas generators  106  are replaced simply by inserting them into tubes  105  through openings  120  after removal of covers  118 . 
     The improved breech mechanism  100  of this invention has several advantages over the existing launch system used for light weight, surface-launched torpedoes. The use of gas generators  106  assures that the firing readiness of the breech does not degrade over time. Moreover, one need not worry about leakage of gas and the resultant injury to personnel which could result. The gas generators  106  are restrained within retaining device  104  and all gases emitted therefrom are directed toward the interior of tube  10 , and not back toward the breech plate  102 . Also, the pressure build-up is directed against the retaining device  104  and breech plate  102 , and not against breech cover  108 . Breech cover  108  is sealed from the interior of tube  10  by breech plate  102 . Gas generators  106  can be replaced in a matter of minutes, as compared to one to one and one half hours it takes to recharge the flasks for all six torpedo tubes normally carried on a typical surface ship. Moreover, corrosion problems evident in the prior art flask are no longer an issue, and maintenance is reduced. The cost of the gas generators is quite low, decreasing the cost of ship operation. Since the gas generators are highly reliable and have a long shelf life, combat readiness is improved. Finally, the improved breech can be retrofitted onto existing tubes, and therefore can be adopted with little or no modification of the tubes of existing vessels. 
     In view of the above description, it is likely that modifications and improvements will occur to those skilled in the art which are within the scope of this invention. The above description is intended to be exemplary only, the scope of the invention being defined by the following claims and their equivalents.