The unfamiliar word stand for Multi Purpose Shelf Mine is an advance type of a sea mine that is moored on the shelf of undersea and targets for the surface vessels with a particular screw sound or the electric field produced by the target ship. I've googled this weapon and managed to get the detailed facts on it. These mines were represented by the PM-1 (acoustic) and PM-2 (under ice antenna-type) influence mines. The mine's antenna system consisted of three antennas: upper, middle and lower, each of which had two electrodes connected with the transformer unit's primary windings. Activation of the influence exploder took place upon the target submarine entering the danger zone. In this system, sea water was used as an electrolyte and the mine's antenna system electrodes functioned as transducers.
These mines were filled with a more powerful explosive charge ("sea mixture") than TNT. Unique devices were developed to enhance the safety of these mines and broaden their planting depth range. Moreover, it was necessary to develop long corrosion-resistant high-strength mine mooring cables. A theory of the mine body strength and buoyancy developed at that time allowed the designers to reduce the weight of the moored submarine-laid mines and increase impact resistance of air-dropped mines. In the 1960s, basically new active mine systems, i.e. wide-band rocket-assisted mines and mine-torpedoes were developed. Mines not only retain advantages over other underwater weapons, but have acquired a new capability to attack remote targets within a relatively short time and with all elements of surprise.
The first active mine systems came into service with the Navy in the early 1970s. They were represented by the PMR-2 antisubmarine rocket-assisted mine, which is unrivaled in the world, and the PMK-1 mine system (the export version of the PMR-2 system), which was basically a combination of a moored mine and a fast underwater automatically targeted rocket, as well as the PMT-1 antisubmarine mine-torpedo (the export version of the PMK-2 system) – a combination of a moored mine and a small antisubmarine homing torpedo. The caliber of the PMK-2 weapon is 533 mm and its length is not more than 6 m. The distinguishing feature of these systems is that though they are basically active mines, they attack targets themselves. The equipment of these mine systems detects and classifies an underwater target, determines its course and running depth, optimizes the target intercept trajectory and generates a command to launch either a rocket, which runs at a speed of about 80 m/s, or torpedo. The warheads (rockets or torpedoes) are accommodated in sealed launchers planted at great depths. There are no effective countermeasures against them today. Operation of the target detection, classification and dynamic parameter determination systems is based on acoustic principles.
Due to the great operational depth, wide target engagement zone and short time of attack, which practically deprive the target of the opportunity to take countermeasures or perform an evasive maneuver, the mine systems have given the Navy capabilities in the performance of antisubmarine missions which no other weapon system of prolonged action against the enemy can provide. Although the emergence of underwater missile carrier spurred the development of antisubmarine mines, the cost effectiveness and the easiness for handling would make MShM very handy weapon in some disrupted water area like Yellow Sea.
