In 1948, work began on the 621 project, which involved the creation of a “special purpose boat.” One of the objectives pursued by the project was to ensure the possibility of a covert approach and a surprise attack on the coastal areas of the likely enemy. In addition, the boats of the project 621, or rather the troops carried on them, could unexpectedly attack the United States Arctic airfields. It was these considerations that ultimately determined the appearance of the promising submarine.
Since the new submarines were supposed to provide an offensive at a distance from their bases, the designers of TsKB-18 (now TsKB MT Rubin) and the command fleet decided that they should transport a sufficient number of soldiers and equipment, as well as fuels and lubricants, provisions, etc. Such a main requirement led to the formation of the main points of the project regarding displacement, dimensions, layout, etc. In addition, serious questions arose about the power plant. The design dimensions directly spoke of the need to use more powerful engines than were available, so I had to start by considering several options.
In the early stages of the 621 project, there were immediately seven options for the design of a promising submarine. However, in the future their number was reduced, and the number of options for a power plant was only three. These options looked like this:
- diesel-electric circuit using a steam-gas turbine for economical operation in a submerged position;
- diesel-electric circuit with a relatively large number of batteries;
- the so-called "single engine" - a diesel engine that worked in all surface and underwater modes. Two options were considered at once: with the absorption of exhaust gases by a special chemical device (ED-HPU) and with their release overboard (ED-VVD).
Calculations have shown that a diesel-electric power plant with a steam-gas turbine will provide the perspective submarine with the greatest range of the underwater course. Therefore, it is such a system that was included in the official terms of reference for the project. However, in the late forties, such systems were only being created and their prospects did not look entirely clear. Therefore, we have foreseen the creation of a backup power plant, which could have been put on the 621 project boats in case of failure of work on combined-cycle turbines. In this case, the submarine would have been equipped with diesel engines and 16 th batteries with 112 batteries in each. It is noteworthy that the design of both variants of the power plant proceeded in such a way that, if necessary, one could be replaced with the other. This was done in the event of the development of a steam-gas turbine and the need to “enter” a new power plant into the boat after the start of mass production.
The landing mission seriously influenced not only the appearance of the power plant of a promising submarine. The placement of a sufficient number of people and technology led to the creation of an original system with five robust enclosures. In the center, almost the entire length, they placed the first robust case. He walked almost from the bow to the stern. On the sides of it, starting from the middle of the boat, there were two additional strong hulls. The front and middle part of the largest hull was placed under the compartments for the landing technology. Its diameter of about 6-7 meters allowed to place in it two decks for equipment. An additional metal “cylinder” was placed on the upper surface of the middle part of the central hull, in which it was planned to arrange a hangar for aircraft.
Part of the landing sites fit into the premises of the central robust hull. There were also premises for the crew of the boat itself. After the landing compartments in the main building there was a central post, and immediately after it there was a compartment for power plant units. There were two diesel engines 37D. Two more 30D diesel engines were located in the stern of onboard sturdy hulls, where two shafts were rotated together with steam-gas turbines. The front two compartments of the side hulls were given to the batteries and balancing tanks required for the landing. All five robust enclosures were connected to each other with transitions, which made it possible to service all the equipment installed in them.
All designs of robust enclosures, according to the project 621, were closed with a single light body. Between it and the robust hulls there was a place for the 29 tanks of the main ballast, three fuel tanks, as well as tanks for balancing and quick immersion. The most interesting part of the light hull was the front ramp. On the bow of the submarine was planned to install 25-meter design, intended for the landing of equipment and personnel to the shore. In the stowed position, the lowered ramp rose to the top position and improved the flow. When disembarking, the submarine had to come close to the shore and lower it to the ground. In order not to damage the light body, its front end had a flat shape and had to be made of armor steel.
The estimated length of the new landing submarine of project 621 was 147,5 meters. With a maximum hull width of 13,3 m, it would have a draft of about 6,3 meters. Estimated displacement with combined-cycle units in the power plant - 5845 tons. When using a diesel-electric system with batteries, this parameter increased by about 630 tons. According to estimates, cargo with a total weight of up to 1550 tons could be placed inside the cargo compartments. The optimal composition of the load was as follows. On the lower cargo deck were ten tanks, in terms of their overall dimensions similar to the T-34, as well as several trucks or armored personnel carriers. On the upper deck, it was supposed to carry only relatively light equipment. In addition to ten tanks, the project 621 submarine could carry up to 12 trucks with soldiers and three trailers, and up to four cars, for example, GAZ-67. Trucks could tow up to 12-14 guns, depending on their caliber. In the upper compartment of the central robust hull, the designers allocated space for three La-11 fighters, upgraded accordingly and had a folding wing. The light hull in front of their "hangar" had a flat surface and was a flight deck. The development of the ejection system was underway. Finally, the submarine provided 745 seats for the transported marines and volumes for the transportation of fuel and lubricants and ammunition.
If necessary, the project 621 submarine could with certain effectiveness protect the landing from aviation enemy and coastal defense. To do this, next to the cabin, two paired anti-aircraft guns of 57 mm caliber and one paired 25 mm, as well as a launcher for rockets were provided.
The practical application of the submarine project 621 was as follows. The submerged boat secretly approaches the shore, and then it floats up and, suppressing the defenses with its own MLRS, literally crawls out onto the shore. The ramp is lowered and tanks, cars, and other equipment are escorted from the cargo compartments of the boat, accompanied by marines. Interestingly, a powerful ventilation system was provided in the cargo compartments to remove exhaust gases. If necessary, the submarine could independently make refueling equipment and provide landing troops with ammunition.
The 621 project can be considered the world's first attempt to make a full-fledged landing ship based on a submarine. The task was very difficult, which is why in the end not a single such submarine was built. Analyzing the finished project, the command of the Navy of the USSR noted a number of controversial issues that required a lot of additional research and work. At the same time, a number of problems were too serious to be solved quickly and easily. Ultimately, the 621 project was closed. As of the mid-fifties, despite the great prospects of such boats, there were no major changes in the direction of fine-tuning the project. At the same time, some constructive developments were later applied in other projects. For example, the submarines of the 941 “Shark” project also have at once five strong hulls connected to each other.
Just a few years after the 621 project was closed, work continued in the direction of the amphibious submarines, but the idea was returned to what was called a roundabout way. At that time, the possibility of creating submarine minelayers was being considered. The need to transport a large number of mines in the end seriously influenced the appearance of 632 and 648 projects. However, over time, the idea of setting up barriers and, as a result, the presence of relatively large volumes on the boat for the payload, was reborn into the concept of a transport submarine. It was assumed that such submarines could not only block the path of enemy ships, but also supply fuel and weapons to their seaplanes, or serve as a floating "warehouse" for rockets and torpedoes. Similar ideas to use submarines for transportation of a fairly wide range of cargoes eventually revived old plans for amphibious submarines.
At the very end of the 50 and the beginning of the 60, the navy again ordered the development of a submarine designed to transport and disembark personnel, equipment and armaments. However, this time the project, which received the index “664”, implied the creation of a boat with a nuclear power plant. It is noteworthy that at the stage of preliminary study of the appearance of a promising boat there were quite serious disputes. The marines demanded an increase in the number of troops carried, naval aviation was pushing for the possibility of supplying aircraft on the high seas, and the naval command tried to “reconcile” all requirements and at the same time not allow the project to become too complicated.
Because of this approach, in the early stages of design, four design options for the design of robust shells were worked out at TsKB-16 (now part of the Malachite). In three versions, differing from each other in layout, the prospective boat had a solid hull of relatively large diameter. In the fourth version of the project, it was intended to use three robust cases at once, arranged side by side and interconnected with each other. In this case, the boat turned out lower and wider than with one large hull.
In December, 1960, TsKB-16, received an order to prepare a set of documents for starting the construction of the first boat of the 664 project. It was required to transfer the drawings to the Sevmash plant until the middle of 1964. As a result of comparisons, a scheme was chosen with one strong case of relatively large diameter. The 664 project was notable for several details from other nuclear submarines. A characteristic feature of this project was the volume in the middle part of the hull, allocated for the payload. As a minelayer, a submarine could carry up to 162 mines PM-1, Serpei, Lira, or UDM. If PM-1, PM-2 or PM-2 mines were used, their number was reduced to 112 pieces. In the case of using the submarine of the 664 project as a transport boat, the compartment contained up to 20 P-5 or P-6 cruise missiles or up to 80 torpedoes of any suitable type 533 caliber. To attack enemy ships or self-defense, it was planned to equip the boat with six torpedo tubes of a millimeter 533 caliber. In the torpedo compartment there was a place for placing 18 torpedoes. Regarding amphibious capabilities accurate data are not available.
Because of the need to transport a relatively large number of mines, missiles or torpedoes, the submarine of the 664 project was supposed to have relatively large dimensions. The length of the order of 140 meters, the diameter of the body - 14 m, draft - about 9,5-10 meters. The estimated submerged displacement of the boat was 10100-10150 tons. The submarine could dive to a depth of 300 meters and accelerate under water to 17-18 nodes. In the middle of the robust hull, closer to the stern, two reactors with steam generating units and turbo-gear units were to be located on the 664 project boat. The movement of the submarine provided two propellers, driven by two electric motors OK-1B power 2200 kW.
Apparently, the development of the use of such submarines as amphibious ships continued until the mid-sixties, when the project was closed. Due to too much load, the CDB-16 simply could not cope with all the tasks. Among other things, he failed to complete the preparation of design documentation for delivery to the plant in time. Nevertheless, the workers of Sevmash began preparations for the construction of the lead ship. They prepared a plaza, ordered metal for buildings and a number of production equipment. Despite the lag on the part of the designers, in 1965, the factory began assembling the first sections of the robust hull. Soon the work stopped. The 664 project was still not ready, and the navy needed new submarine missile carriers. In 1966, the project was closed for hopelessness. All construction work was terminated in November 1966.
By this time, several converted diesel-electric submarines experienced fuel transfer from one submarine to another. The tested system was recommended for installation on submarines of the new 664 project and the available diesel-electric ones, which were supposed to be refueled directly into the sea. As for the transportation and landing of troops, then, judging by the available data, by the end of development this function was abandoned. When placing a cargo compartment in the middle part of the submarine was unlikely to be able to disembark tanks, cars or armored vehicles that do not have the ability to cross water bodies by swimming. In addition, the hull and draft lines of the 664 submarines of the project speak directly about the impossibility of reaching the shallow water. Probably, if the project had followed the path of using three solid hulls, the designers would have been able to achieve the initial tasks, which meant not only setting up minefields, but also transporting personnel and armored vehicles.
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