EP0524232B1 - Process for repelling torpedoes - Google Patents

Abstract

The invention concerns processes for luring torpedoes approaching a ship (10). It consists in equipping a known decoy (1) with an explosive charge (6) and a sonar (7) for the detection of the torpedo as it passes (3) in the vicinity of the decoy. The charge is explosed when the torpedo is at the nearest point, the explosion causing the destruction of the torpedo. The invention combines the task of decoying with that of destroying.

Description

The present invention relates to methods which make it possible to fight against torpedoes, more particularly by attracting them towards a fictitious goal distant from the boat on which they were fired.

It is known in the military art to lure the enemy by presenting him with false targets which he confuses with the real ones and on which he concentrates his shooting, which does not present risks for the real target. This is how planes can drop fireworks which emit a lot of infrared, which attracts missiles guided by infrared. In the naval field, we also know how to deceive torpedoes, in particular those of the passive type, by dropping a buoy which emits acoustic signals resembling those of the carrier ship, but at a level clearly higher than the latter. The torpedo goes towards this buoy, and when it arrives near it the building is far enough away to considerably reduce the risks of being hit. However, the risk is not zero because we can very well, using a relatively basic logic, when the torpedo has passed the buoy redirect it by making it describe a circle towards another source which may be the carrier ship . Furthermore, if the carrier ship is part of the escort of a convoy, there is a great risk that the torpedo after passing the lure will be guided towards one of the ships of the convoy, since these ships remain in principle relatively grouped.

US Patent 4,215,630 describes a system of this kind in which a missile is launched on the path taken by a torpedo in front of it. This missile includes an acoustic rocket which monitors the approach of the torpedo and detonates the missile when this torpedo passes closer. However, nothing is planned to choose an adequate recurrence frequency for the rocket.

The features of the independent claim define the preferred embodiment of the invention.

• la figure 1, une vue de côté d'un leurre attirant une torpille pour la détruire ; et
• la figure 2, une vue de dessus d'un bâtiment remorquant un leurre et des moyens de surveillance et d'alerte.

Other features and advantages of the invention will appear clearly in the following description given by way of nonlimiting example with regard to the appended figures which represent:

• Figure 1, a side view of a lure attracting a torpedo to destroy it; and
• Figure 2, a top view of a building towing a lure and monitoring and alert means.

There is shown in Figure 1 a lure 1 which has been dropped by a carrier building after detection of the arrival of a torpedo 3. This lure is positioned by means of a float 50 and a rope 51 to low immersion under the wake 53 of the carrying building, on the one hand to prevent the torpedo from distinguishing it from the carrying building by locating too much immersion and on the other hand to have sufficient immersion to avoid being drowned in the wake whose acoustic characteristics are very different from those of the marine environment. The torpedo 3, initially fired against the carrier building, is attracted to the lure 1 along a trajectory 4 which is shown to be substantially rectilinear in the vicinity of the lure, the torpedo having then joined its attack immersion. After passing as close as possible to the lure at a distance d, the torpedo continues its course if nothing else happens.

The lure 1 comprises electronic equipment making it possible to generate acoustic noise in a frequency range corresponding to the operating frequency bands of the torpedo seeker, for example between 15 and 80 kHz. Hydrophones not shown make it possible to emit these acoustic signals in a substantially isotropic manner in the sea.

According to the invention, the lure 1 also comprises an explosive charge which makes it possible to destroy, or at least to neutralize, the torpedo by exploding when the latter passes close enough to the lure. Compared to electronic equipment, this charge is arranged so as to generate, during the explosion, a substantially isotropic shock wave within a radius sufficient to destroy or neutralize the torpedo in the majority of cases. For example, the explosive charge may consist of 150 kg of a powerful explosive, which makes it possible to obtain a radius of neutralization of the torpedo of the order of 10 to 15 m. We can then call this device "decoy-trap".

• la portée maximale recherchée étant faible, de l'ordre de 2 à 3 fois la distance léthale de la charge, soit environ 40m, les impulsions émises doivent être très courtes, d'une durée de quelques ms par exemple ;
• il faut éviter de détecter la torpille sur des échos croisés à des distances double ou triple de la portée maximale visée, ce qui est obtenu par l'absorption élevée de l'eau de mer dans la gamme de fréquences ainsi utilisée ;
• il est également nécessaire d'éviter que d'autres leurres mis à l'eau séquentiellement dans le temps à plusieurs centaines de mètres les uns des autres ne viennent perturber réciproquement leur fonctionnement, ce qui est également obtenu par l'absorption du signal du sonar dans l'eau de mer.

According to the invention, the lure 1 is provided with detection equipment essentially consisting of an active sonar which comprises a set of additional hydrophones 7 distributed over the wall of the lure so as to constitute an omnidirectional sonar making it possible to detect the passage torpedo. The operating frequency of this sonar is chosen to be relatively high, for example of the order of 400 kHz, so that the operation of the active sonar is not hampered by the proper emission of the acoustic decoy. Besides this main reason, other considerations lead to choosing such a high operating frequency:

• the maximum range sought being small, of the order of 2 to 3 times the lethal distance of the charge, or about 40m, the pulses emitted must be very short, of a duration of a few ms for example;
• it is necessary to avoid detecting the torpedo on crossed echoes at double or triple distances from the maximum aimed range, which is obtained by the high absorption of seawater in the frequency range thus used;
• it is also necessary to prevent other lures launched sequentially in time several hundred meters from each other from interfering with their operation, which is also obtained by the absorption of the sonar signal in sea water.

Correlatively to this characteristic, the active sonar also has a high repetition frequency, consistent with the maximum target range, for example around twenty transmissions per second. Such a cadence allows, taking into account a torpedo speed which can reach in the known models 25 m / s, to obtain a sufficient number of echoes, for example 5 to 10, to be able to determine the instant of passage at the nearest point, known by the abbreviation CPA, and thus cause the charge to explode at this instant.

It is important to determine this CPA to obtain maximum effectiveness of the trap lure by detonating it when the torpedo / lure distance is minimum. To determine this instant, the speed of variation of the distance is measured, and when the latter falls below a determined threshold the sonar causes the order to ignite the load.

It is also necessary to discriminate the echoes coming from the torpedo from the parasitic echoes returned by the surface of the sea and by the wake, which are in the field of action of the sonar. For this, the sonar uses the Doppler effect on the received echoes, which is a function of the radial speed between the sonar and the torpedo. Given the large difference in the Doppler shift, resulting from the choice of a high operating frequency and a narrow spectrum of the signal transmitted in pure frequency, this Doppler shift remains large and determinable until shortly before passing in the CPA, or in a known way it becomes null. When therefore discrimination is no longer possible, the torpedo is very close to the CPA and it is then legitimate to trigger the explosion of the charge which, taking into account the different delays of the organs in question, and possibly with the addition of 'a small delay, causes very noticeably at the CPA.

With these characteristics, such an active sonar can be brought to detect fish or marine animals, dolphins for example, which pass near the lure and whose the dimensions and speed characteristics are close to those of torpedoes.

The risk of thus causing an untimely explosion can be considered acceptable when the lure-trap implemented after a torpedo alarm in the carrier building has an operating time limited in time, which is the case when it is released hopeless to get it back.

This risk is however unacceptable in the case where the operating time is significant, which is in particular the case when the trap decoy is towed behind the carrier boat in order to be used in preventive mode without torpedo warning information.

This problem can be solved using at least two types of solution:

In a first solution, valid both in the case of the dropped lure and in that of the towed lure, the lure is equipped with detection means making it possible to detect the noise radiated by the torpedo. These detection means include a set of hydrophones placed on the decoy so as to provide substantially omnidirectional reception coverage, and a receiver connected to these hydrophones and covering a wide but sufficiently low frequency band, a few kHz at most, so as not to not be bothered by the clean emission of the lure.

The minimum reception range of this device is defined for a low-noise torpedo and in the most unfavorable sea conditions (force 6 for example), so as to correspond substantially to the range of the active sonar. These detection means intervene in the logic for igniting the explosive charge so as to inhibit this ignition, which is normally caused by the reception of the active sonar, as long as the detection means do not receive a radiated noise corresponding to a torpedo.

In addition, to avoid the noise radiated by the load-bearing building being confused with the noise of a torpedo, the variation in the noise reception level is measured, so that it is not recognized as coming from a torpedo that when it has a positive gradient corresponding to the approach of this torpedo towards the lure, while of course the level of noise radiated by the carrier building remains substantially constant.

A second solution, which only works in the case of the towed trap lure, is shown in FIG. 2. It consists in towing behind the load-bearing vessel 10, in addition to the trap lure 1, a device 11 for listening to the noise radiated by the torpedo. This device is towed so as to be located between the lure and the boat at a distance 1 from the latter while the lure is at a distance L. In this way, by placing the hydrophones in the listening device 11 so to cover an area 12 surrounding the lure and in which the boat is not located, the noise caused by it is not received by the listening device and therefore does not interfere with it.

Such a device makes it possible to activate the active sonar of the lure-trap only after having detected the noise radiated in the field of action 12 of the listening device. The torpedo is attracted to the lure which has been put into permanent operation in a preventive manner without torpedo alert information, and when it enters the zone 12 it is detected by the device 11 which activates the sonar of the lure via signals passing through the trailer cables. These trailer cables also make it possible to supply electrical power to the decoy trap and the listening device, and to transmit various signals, such as particularly the signals for monitoring the various functions of the decoy and the listening device. In the same way as in the first solution, the effective authorization to ignite the charge explosive by the active sonar is transmitted only in the presence of radiated noise detected by the listening device 11.

The trap decoys thus described can be used in different ways, both to protect surface vessels and submarines. With regard to the protection of surface buildings, two techniques can be distinguished:

First of all, the autonomous lure-trap which can be released from the rear of the building and which is implemented after a torpedo alert obtained according to ordinary techniques, most often starting from the detection of the noise radiated by the torpedo. Such a decoy trap includes, as shown schematically in Figure 1, a main body of cylindrical shape terminated by two truncated cones. The cylindrical part 54 contains the explosive charge, while the end cone trunks 55 and 56 contain the electronic equipment comprising the organs of the acoustic decoy, the active sonar and possibly the radiated noise detector. This electronic equipment is connected to hydrophones such as 7 distributed adequately over the surface of these truncated cones to obtain the desired receptivity characteristics. The emitter of the acoustic lure is advantageously at the end of the lower cone 56 in the form of a ball comprising acoustic transducers giving a substantially spherical radiation pattern, except upwards which is immaterial since the torpedo will not come not over there.

To drop this lure-trap from the building, for example, we use a device similar to underwater grenade launchers and the activation of the lure is done at this time, taking into account a set of safety devices that allow not not cause the explosion by detecting the building width. The fires include, for example, mechanical safety which is extracted at launch using a metal cable called armament wire connected to the building, hydrostatic safety which is triggered when the lure-trap has reached its operating immersion , and security electronic which provides a time delay allowing the carrier building to move away.

Such a trap lure is not only effective against acoustic torpedoes, but also against so-called wake torpedoes which raise the wake of the building. In fact, as it is dropped into the wake at a low immersion below it, it can detect the torpedo when it passes nearby, the wake having limited dimensions both in the horizontal plane and in immersion, which are mostly ordinary buildings within the detection limits as determined above.

In another embodiment, corresponding to FIG. 2, the lure-trap is towed behind the building in a systematic manner when one is in a dangerous zone and without waiting for there to be a torpedo alert.

This trap lure then being towed by a boat must navigate at a relatively low immersion, for example 10 to 15 m, and it is therefore preferable to give it buoyancy and hydrodynamic characteristics favoring this towing. For this, it is given a substantially neutral buoyancy and it is fitted with a control system operating on the basis of the indications of a pressure sensor which indicates the immersion reached. These control means then allow for example to adjust the fins fixed on the main body, which allow to maintain the desired immersion. As in the previous example, the main body includes the explosive charge, the acoustic lure and the active sonar. Depending on whether or not a "fish" 11 is used making it possible to detect the noise radiated by the torpedoes, a radiated noise detector is included in the lure or not. In addition, as this lure is intended to be recovered on board the carrier vessel, it is provided with specific security systems which are reversible so as to be able to recover it without risk of explosion. Control signals transmitted by the trailer cable make it possible to activate and deactivate these means of security. As additional security, the operating status of these security means is monitored by circuits located in the decoy and the results of this monitoring are relayed to the boat via the towing cable.

To protect using submarines against submarines intended to attack them, the most advantageous method consists in using a trap decoy adapted to be launched using the torpedo tubes of the submarine. marine.

The structure of such a lure can be similar to that of the first embodiment described above, but it is preferable to construct it in such a way that the buoyancy is substantially neutral as in the second embodiment in order to allow it to float between two waters, substantially at the submerged level of the submarine when it has dropped it. As such buoyancy is very difficult to obtain, an advantageous improvement consists in distributing the masses inside the lure in such a way that it is held in a vertical position and in providing it with a small propeller located at one of its extremities and being able to function in a reversible manner, so as to drive it up or down depending on whether the real buoyancy in operational conditions will tend to make it go up or down.

Similarly when it is ejected from the tube the lure should normally be found at the rear of the submarine when it progresses, to prevent it from hitting the submarine during overtaking, at the risk of triggering a accidental explosion. For this, the lure can be fitted with slightly offset fixed fins so that, taking advantage of the speed acquired during launch, the lure deviates slightly from its direction and deviates from the trajectory of the submarine.

The lure is of course provided with a set of safety devices similar to those which have been provided in the first mode of implementation described above, but since immersion safety is no longer useful in this case, it can advantageously be replaced by a mechanical delay which authorizes the arming of the detonators only after a fixed term.

Claims (11)

1. Method of combatting torpedoes, of the type consisting in attracting the torpedo (3) by a decoy (1) emitting an acoustic decoying signal, in equipping this decoy with an explosive charge (54), in detecting (7) the passage of the torpedo in proximity to the decoy by using an active sonar (7) placed in the decoy (1), and in then causing the explosive charge to explode during this passage in order to destroy the torpedo, after having monitored the reduction in the distance between the torpedo (3) and the decoy (1) in order to trigger the explosion when the torpedo passes closest to the decoy, characterized in that the recurrence frequency of the emissions from the active sonar (7) is chosen to make it possible to obtain a number of echoes on the torpedo which are sufficient both to determine this closest passage, and avoid long-distance detection by crossed echoes.
2. Method according to Claim 1, characterized in that, as the acoustic decoying signal is emitted in the reception frequency band of torpedo homing heads, the operating frequency of the active sonar (7) is situated above the frequency of the acoustic decoying signal, with a separation which is sufficient so as not to be disturbed by the decoying signals.
3. Method according to either of Claims 1 or 2, characterized in that the said sonar (7) is substantially omnidirectional, and that the doppler effect is used on the echoes originating from the torpedo (3) in order to discriminate the latter from echoes due to the surface of the water (2) and to the wake of the vessel (53).
4. Method according to any one of Claims 1 to 3, characterized in that the noise radiated by the torpedo (3) is furthermore detected in order to allow the explosion of the destructive charge only in the presence of this radiated noise, which makes it possible to avoid triggering this explosion on detection of a fish or of a marine mammal.
5. Method according to Claim 4, characterized in that this radiated noise is detected with a substantially omnidirectional reception characteristic, in a band of frequencies lower than the transmission band of the acoustic decoy in order not to be disturbed by this transmission band, and that the reception threshold is set to correspond to a range substantially equal to the range of the active sonar for a low-noise torpedo and a heavy sea.
6. Method according to any one of Claims 1 to 5, characterized in that the decoy-trap is independent and that it is jettisoned at the rear of the carrying vessel.
7. Method according to any one of Claims 1 to 6, characterized in that the decoy-trap is towed at a shallow depth under the wake of the carrying vessel (53) with the aid of a towing cable behind this carrying vessel.
8. Method according to any one of Claims 1 to 7, characterized in that safety devices are used, making it possible to avoid causing the decoy-trap to explode on detection of the carrying vessel.
9. Method according to Claim 8, characterized in that a mechanical-arming safety device, triggered upon jettisoning, a hydrostatic safety device triggered by the pressure corresponding to the operating immersion, and a safety device by time delay determining a safety delay between the moment of jettisoning and the moment of switch-on are used.
10. Method according to any one of Claims 1 to 5, characterized in that the decoy-trap is towed behind the carrying vessel and that the latter furthermore tows, between the decoy-trap and itself, a device (11) making it possible to detect the noise radiated by the torpedo and to order the active sonar of the decoy-trap to be switched on.
11. Method according to any one of Claims 1 to 5, characterized in that the decoy-trap is ejected by the torpedo launcher tube of a submarine, and that means are used making it possible to keep this decoy-trap in substantially zero buoyancy at an immersion depth corresponding to that of the submarine.