In the late 1980s, the Yugoslav Navy considered the development of universal weapons, which were planned to equip combat swimmers. This weapon was supposed to shoot both under water and over water, and be silent. There was also a requirement for the possibility of firing a weapon with gloves. By that time, the Heckler & Koch P11 underwater pistol, which was strictly classified, had already become widespread in the West. At the same time, in the countries of the Eastern Bloc, such pistols were practically absent at that time.
At the same time, Yugoslavia has always shown a certain independence from the defense industry of the Warsaw Pact countries in the weapons-technical respect. For this reason, when creating weapons that were intended to arm combat swimmers, in Yugoslavia went their own way. Because of the internal contradictions that began to accumulate in Yugoslavia, and also because it was necessary to create weapons in a short time and inexpensively, and also to do it secretly, the secret service of the Navy of Yugoslavia placed an order for weapons in the Austrian city of Linz . This KB had a great experience in creating weapons. In those years, such developments in cooperation with foreign specialists were common for Yugoslavia.
The advanced tactical and technical requirements for a new weapon looked like this:
- the possibility of using under and above water;
- small dimensions;
- reduced shot sound;
- effective range under water - 10 meters;
- effective range over water - 20 meters;
- water resistant at depths up to 40 meters / pressure up to 5 bar;
- the possibility of using weapons in diving gloves;
- The weapon was supposed to ensure the penetration of the standard scuba diving cylinders.
The assigned task did not frighten the representatives of the EBW design bureau from Austria and the design bureau experts successfully coped with it. Moreover, virtually no new weapons have been developed. In fact, the Austrian designers have developed only a special ammunition that could be used with all types of signal pistol, having a caliber 26 mm. Thus, the Austrian development in the interests of the Navy of Yugoslavia SSU (Self Supressing Unit) looks very much like a signal pistol. The fact that before us is something else, said only the arrow sticking out of the sleeve. To disperse the swept bullet used up to speeds up to 310 m / s, we had to use a special design of the cartridge case, since the maximum pressure that occurred in the bore of the signal pistol was only 110 bar.
It should be noted that from a technical point of view, the underwater projectile could be accelerated to speeds of more than 310 m / s, but in this case it would not be noiseless. The sound of a shot includes the 2 component: a sonic boom that appears when a bullet passes through a sound barrier and a gas bump is the noise of gunpowder gases rushing out. If the gas blow can be compensated by using a silencer, the sound impact is not. It is for this reason that the ammunition used in the SSU submarine pistol should have a subsonic speed.
SSU special munitions were made on the principle of high / low pressure pipes. This principle was developed as early as the Second World War in Germany, it was used to achieve the highest possible flight speeds with uniform and as low as possible pressure. In this case, the ignition of the powder occurred in the so-called part of the high pressure, which was connected with the barrel of the weapon (low pressure area) by several or one small hole. In the SSU, at the moment of ignition of the powder, pressure was generated up to 1200 bar, however, in the low pressure zone, which was connected to the high pressure area using four nozzles, the pressure was already less than 100 bar.
Due to this effect, boom acceleration was carried out evenly and "slowly." At the same time, the high-pressure chamber had a length of 10 mm and a diameter of 9 mm. Its volume was equal to the volume of the .38 Special caliber case. The ammunition developed by Austrian specialists was planned to be equipped with standard nitroporoch, however, the ignition process itself was implemented in a very original way. In the event that the powder was ignited in an ordinary way - by the method of pricking the cap of the cap, there would be a real danger that under pressure when the membrane was pierced, unburned powder granules could somehow end up in the nozzle holes, thus blocking them. At the same time, a further increase in pressure would be an uncontrollable process, which in turn would be a reason for reducing the accuracy of fire. It is for this reason that the charge of gunpowder in the SSU submarine pistol ammunition ignited in front.
To achieve this, the flame of a standard magnesium capsule was fed directly to the nozzles using a special “incendiary barrel”, which at the same time served as a nest for a capsule sleeve. Here the flame changed its direction, forcing the battle charge to burn out from the front. Despite this, the resulting pressure could not come out in front through the four nozzles available, since a special strong membrane made of plastic 0,6 mm thick was installed in front of them. The use of this membrane led to the fact that the pressure in the high-pressure chamber was sufficient for pure combustion of gunpowder.
Since the ordinary magnesium capsule was not waterproof, it took a non-standard solution aimed at preventing water from entering the cartridge from the back. To solve this problem, Austrian designers from EBW created a transition drummer. This drummer was used only to transfer the kinetic energy from the underwater pistol trigger inside the cartridge. At the moment of firing, powder gases with a very high degree of compression after penetration of the membrane exited to the low-pressure zone through the nozzle. This zone had a diameter of 20 mm and a length of 110 mm. In standard high / low pressure pipes, the low pressure area serves as a barrel, but in the SSU submersible pistol, in which an arrow of 8,7 mm thickness is used, this area was significantly larger. This was largely due to the suppression of the noise that was produced during the shot.
The idea of Austrian specialists was to prevent hot, expanding powder gases from escaping, intercepting and blocking them inside. For this, a piston was used. The piston was located directly in front of the nozzles, it served to seal the low pressure area. The piston was set in motion by using hot powder gases that were flowing from the nozzles. In front of the piston in the center was the receiver of the tail part of the shot arrow, which he accelerates during his movement. In this case, the front guide of the boom is a hole, which is drilled in the head part of the cartridge. A special O-ring was put on the boom, which prevented water from entering the low pressure zone. At that moment, when the piston reached the extreme forward position under the influence of gases, pushing the boom in front of it, it rested against the front edge of the low-pressure chamber from inside, thereby preventing the exit of powder gases through the barrel of an underwater pistol, making the gun shot as quiet as possible.
When developing an SSU underwater pistol ammunition, high water density was taken into account, which has a very significant impact on their design. All underwater shooting ammunition is made as thin and long as possible, that is, arrow-shaped. In the case of the Yugoslav SSU, these are arrows that have a length of 122 mm with a diameter of 8,7 mm. In this case, two types of arrows were created, which differed from each other only in the strength of the rod used. The arrows of the first type behind the hardened steel head had an aluminum rod with a wall thickness of just 0,5 mm. The arrows of the second type were distinguished by a greater wall thickness of the tail — 1,75 mm. The mass of ammunition was 12 and 21 grams, respectively. In flight, the stabilization of the created shells occurred along the arrow principle, as well as for the shells of shotguns, which were widely distributed from 1910 onwards.
After 5 prototypes were created, a decision was made to conduct their tests in order to make sure in practice that they meet all the requirements of the specification. Since the city of Linz was not far from Salkammergut with its deep lake, they decided to approach the solution of the problem very pragmatically in the EBW design bureau, they just rented a water bike and went to the lake. In the middle of the reservoir, with the help of a rope, the unloaded cartridge dropped to a depth of 20 and 30 meters. After that, it was removed from under water and spent external drying. Then the body of the cartridge was disassembled and the tightness of the structure was checked. Approximately 8 hours of work under the scorching sun took to make it finally clear that the principle of sealing will be maintained at a depth of 70 meters, as well as at a pressure that is higher than the required by 60%.
Then, of course, it took a series of firing tests. Shooting was carried out from a massive launcher. Shooting proved the fact that the dimensions of the body of the cartridge were calculated correctly. The hull was so strong that you can shoot a cartridge from SSU even without a barrel, despite the pressure in the 1200 bar in the high-pressure zone. With this, only the trigger release made itself felt, this sound was louder than the shot itself. During the tests, shooting was conducted on standard scuba tanks made of steel. In all cases, without exception, these cylinders were pierced.
A check on the convenience of servicing an underwater gun in thick diving gloves showed that the weapon was easy enough to use, the test was simple. At the same time, accuracy tests had much higher requirements. It was relatively easy to verify the accuracy of SSU, which was fixed in a special machine. But for the developers of EBW, real shooting sensations were important. In this case, the characteristics of a shot from this underwater gun can be described as very unusual. Although at the first moment the SSU has an average power (for a signal pistol) recoil force, at the moment when the piston beats into the front wall of the liner, there is a counter-moment, which is much more noticeable. At the same time for the weapon at the time of the shot it does not matter.
When it turned out at the very beginning of 1991 of the year that the situation in Yugoslavia was leading to civil war, the development of the SSU submarine gun was almost immediately stopped by both the Yugoslav Navy secret service and the EBW development company. At this point, it was possible to collect all the 5 suitable for conducting shooting samples of the gun. Three of these prototypes were turned into special split weapon models.
In terms of technology, SSU development has been completed. The cartridge could be put into mass production. The changes could only relate to the use of different materials, since in the process of production all the steel parts, with the exception of the high-pressure chamber, which was made of special high-grade steel, could be replaced with plastic and aluminum, which had the best resistance to saltwater.
As a result, this weapon turned out to be unclaimed neither by the Navy of Yugoslavia (the country was falling apart), nor by the Warsaw Pact countries. At the same time, in the USSR, by that time, new, more promising models of weapons were created for underwater shooters, including store-type samples. At the same time, the practice of recent decades shows that maritime units for special purposes, and with them, underwater military operations in so-called asymmetrical military conflicts play practically no role. In this aspect, the created SSU is an original development, a good weapon-technical idea, which, having proved its technical soundness, did not go into the series.