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Project 678 / Project 1851
Nelma class / X-Ray class

Project 1851 / Project 678 X-RayThere is considerable obscurity concerning this small class of small submarines, starting with the project designation. Some sources reference the X-Ray class as Project 678, while more authoritative sources reference it as Project 1851. Both project numbers seem to be associated with this program, though what difference they make is opaque.

Some sources suggest that this class consists of a single unit, while other sources suggest that this class consists of three units. By one account this submarine was built at the Admiralty Yard in St. Petersburg in 1982, while others have starting in 1981 and running through 1995. The most authoritative sources tend toward a multi-unit class. Some source suggest the boats are some 63 meters long with a submerged displacement of 1,450 tons, while others report a design some 40 meters long with a submerged displacement of 1,000 tons. Opinions on whether the class is one or three units is independent of the length and displacement of the vessel. On balance, the smaller design seems associated with the roject 678 / Project 1851 Nelma class / X-Ray class nomenclature, while the larger design seems to be the Project 1083 Paltus / 10831 / Norsub / Nor-Sub-5 program.

Initially, in 1980 Sudomech in Leningrad began construction of a series of nuclear submarines special project 1851, deprived of weapons. The ships were intended, in particular for deepwater operations using divers equipped with a pressure chamber. The first submarine AS-23, was laid Sept. 25, 1981, launched on 30 October 1983 and joined the Northern Fleet on Dec. 30, 1986 It was followed by AS-21 (incorporated December 26, 1984, launched 29 April 1991, came into operation on Dec. 28, 1991). Completed a series of AC-35 (incorporated December 20, 1989, launched 29 September 1994 and came into operation on Oct. 12, 1995). The ships are equipped with a reactor capacity of 10 MW. According to NATO classification they are given the designation X-Ray.

The inconnu (Stenodus leucichthys) is a species of freshwater whitefish of the family Salmonidae. It is also known as the "coney", nelma, belorybitsa, or sheefish. It is the only species in the genus Stenodus. Salmo Nelma is a silvery white Salmon, with greatly elongated head, and lower jaw much longer than the upper. Length from three to six feet: snout depressed: mouth rather large, and furnished with large lateral laminae: scales large: tail forked. Inhabits the larger rivers of Siberia.

This class was designed for operations with divers equiped with a pressure chamber. The Project 678 X-Ray class submarine is a small, nuclear-propelled boat that is geneally generally similar in concept to the US Navy's NR-1 submersible. It was probably designed for covert underwater intelligence collection [ "research" or "ocean engineering").

Deep diving enclosures that provide an environment at normal or near normal atmospheric pressure include diving suits, diving chambers and other occupant enclosure devices, as well as crewless enclosure devices falling within the term "submersibles." A wall structure in accordance with the invention is also suited for use in forming at least a part of an enclosure for containing vacuum conditions.

At depths below 1,200 feet a diver needs almost all his energy to breathe, and consequently his work effort diminishes with depth. Furthermore, long-term operations at pressure create several immediate problems, such as rescue in the event of injury, and the long-term effects under such conditions are still not fully known. A diving suit capable of providing internal pressure equivalent to one atmosphere would enable a diver to carry out a high percentage of his normal duties at depths below 1,200 feet, whilst reducing many of the dangers that are at present inherent.

It is essential to produce a one atmosphere diving suit with a good strength to weight ratio. This is particularly true of the limb portions of the suit, since having commenced movement of a limb portion, such as an arm, the momentum of the moving mass of the limb tends to cause it to move beyond its objective, or overshoot, thus making the accomplishment of intricate tasks difficult, time-consuming, and tiring if moved by the physical effort of the diver. In present-day diving suits high strength to weight ratios are obtained by the use of magnesium with, however, the constant risk that in an undersea environment any break in the protective treatment of the metal will lead to corrosion followed by rapid disintegration.

The small 'X-Ray' class special missions submarine had become inoperable by 1997 and will not return to service.



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