Alfa class submarine

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Image:Alfa class submarine 2.JPG The Soviet Union/Russian Navy Project 705 (Lira) was a submarine class of hunter/killer nuclear powered vessels (Podvodnaya Lodka Atomnaya). The class is also known by the NATO reporting name of Alfa. They are the fastest and one of the deepest diving military submarines built, second only to K-278 Komsomolets in crush depth.

1 Preproduction
2 Production
3 Strengths and failures
4 Decommissioning
5 General characteristics
6 Alfa class submarines in fiction
7 External links

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Preproduction

The initial design work began in 1957 and was highly innovative. A special titanium alloy hull would be used to create a small, low drag, 1,500 ton, three compartment vessel capable of very high speeds (in excess of 40 knots) and deep diving. The submarine would operate as an interceptor, staying in harbour or on patrol route and then racing out to reach an approaching fleet. A high-power liquid-metal-cooled nuclear plant and extensive automation would also greatly reduce the needed crew numbers to just 16. The real-life problems with the design became quickly apparent and in 1963 the design team was replaced and a less radical design was proposed, increasing the vessel weight by 800 tons, increasing all main dimensions and doubling the crew.

A prototype, Project 661 or K-162 (since 1978 K-222) (referred to by NATO as the Papa class), was built at the Sudomekh yards in Leningrad and completed in 1972. The long build-time was caused by numerous difficulties in manufacture and design flaws. Extensively tested and reconfigured it was scrapped in 1974 following a reactor accident. It reportedly had a top speed of 44.7 knots and a claimed dive depth of 800 m. This combined with other reports created some alarm in the U.S. Navy and prompted the rapid development of the ADCAP torpedo program and the Sea Lance and W-class submarine projects (the latter two were cancelled when more definitive information about the Soviet project was known).

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Production

Image:Alfa class submarine.JPG Production started in 1974 as Project 705 with construction at both the Admiralty yard, Leningrad and at Sevmashpredpriyatiye ("North Machinery Factory"), Severodvinsk. The first vessel was commissioned in 1977. In 1983 with the completion of the seventh vessel production ended. All vessels were assigned to the Northern Fleet.

It appears that the capabilities of the vessels were over-estimated and that they suffered from a number of problems. For a submarine, it was dangerously noisy at high speeds, yet these high speeds proved important in outrunning anti-submarine crafts, resulting in this sacrifice of sound for speed. Aside from this, the 155 MW BM-40 reactors proved to be unreliable—the liquid metal coolant often leaked and could solidify if the system did not run constantly to avoid this.

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Strengths and failures

Project 705 boats consisted almost entirely of most modern possible, custom-developed and therefore untested solutions. They were intended to be an experimental platform themselves, to test and rectify all the innovations, which would afterwards start a new generation of submarines. Highly experimental nature mostly predefined their future, and the proposed new generation never came beyond this experiment due to end of the Cold War.

Specially for this submarine two nuclear reactors were developed indepently, BM-40A and OK-550. Both were lead cooled fast reactors, which was a very innovative solution, used before only on Project 645. Both reactors used an eutectic lead-bismuth solution for the primary cooling stage. OK-550 was used on 705, but later, on 705K, BM-40A was applied due to OK-550 low reliability. BM-40A provided the boat with 155 MW of power, similar to a battleship, and as a result burst speed at full load reached 40 knots. The reactor could quickly adjust it's power output, so boat was able to switch between cruising (up to 22 knots tactical speed) and burst speed in about a minute, unlike ships and submarines with typical water-cooled reactors requiring 15 to 30 minutes. Burst speed in tests was between 43 and 45 knots for all vessels. Propulsion was provided by the main propeller with 30-MW steam turbines, and two 100-kW electric-powered propellers served as an additional propulsion for maneuvering and a backup. Backup power systems included a 500-kW diesel generator and a set of zinc-silver batteries.

However, BM-40A turned out to be not very reliable as well, and very expensive in maintenance. The lead/bismuth solution solidifies at 125 degrees C. If it ever hardens, it will be impossible to restart the reactor, for the fuel assemblies will be frozen in the solidified coolant, so, whenever the reactor is shut down, it must be heated externally with overheated steam. Near the piers where the submarines were moored, a special facility was constructed to deliver superheated steam to the vessels' reactors when the reactors were shut down. A smaller ship was also stationed at the pier to deliver steam from its steam plant to the Alfa submarines. But, because coastal facilities were treated with much less attention than the submarines, they often turned out to be inable to reliably heat the submarine reactors, and they consequently had to be kept running even while they were in harbour. The facilities completely broke down early in the 1980s, and since then, the reactors of all of the operational Alfa submarines were kept constantly running. While the BM-40A reactors are able to work for many years without stopping, they were not specifically designed for such treatment, and any serious reactor maintenance became impossible. This led to a number of failures, including coolant leaks and one reactor broken down and frozen in sea, but, however, constantly running the reactors proved better than relying on the coastal facilities. Four vessels were decommissioned due to freezing of the coolant.

Both OK-550 and BM-40A reactors are single-use reactors and can't be refuelled, because the coolant would inevitably freeze in the process. This was compensated by a much longer lifetime on their only load, after which reactors were completely replaced. While such a solution potentially can decrease service times and increase reliability, it's still more expensive, and the idea of single-use reactors was unpopular in 70s. Besides that, K-705 didn't have a modular solution which would allow to quickly replace reactors, and such maintenance was as long as for a usual submarine.

All possible systems on the submarine were automated, and it actually required only 14 crew members to operate. Other crew members served as the second shift or as a reserve. While the initial design provided less than 20 members, all officers except the cook, it was considered more practical to have more reserve. Most of the electronics were newly developed, and failures were expected. Certain reliability and efficiency problems were reported with the weapon and detection systems, in part because of the electronics, and it's possible that some accidents could be predicted with better developed electronics. Overall, though, it performed quite well for an experimental system.

Except the testing vessels, Project 705 and 705K submarines were built with titanium hulls, which was revolutionary in terms of submarine design at the time, due to the cost of titanium, technologies and equipment needed to work with it. The internal strong hull was separated into 6 watertight compartments, of which only the third (center) compartment was manned, and others were accessible only for maintenance. The third compartment had reinforced spherical bulkheads, which could withstand the pressure at the test depth and offered additional protection to the crew in case of attack. To further protect the crew, the ship was equipped with a protected rescue capsule for all the crew which could be ejected in very hard conditions. The hull had very high strength reserve for higher depths, and according to some information one of the submarines was tested on depth up to 1300 meters. These submarines could never make use of it for stealth purposes, though, as submerging to such depths and returning causes permanent damage, which in a few cycles would make the vessel very unreliable; possibly this test was committed just before decomissioning. Also, at first the hull was quite imperfect, and the first submarine was quickly decommissioned because of hull cracks.

Despite the constant reliability problems of vessels themselves, no crew members were lost on these submarines. This is due to extensive crew protection measures and unprecedented automation, which allowed to isolate the crew from most of the machinery.

While such measures sacrificed some of the technical characteristics, the negative effect was reduced by smaller crews. They were not only a protection for experimental vessels, but were viewed as one of the distinctive features of new-generation submarines, adopting the aircrafts' concept of a fully automated vessel with minimal, but highly trained crew. The concept of an underwater fighter went to tactics as well. The boat is very maneuverable for it's size, making a 180 degree turn at full speed in 40 seconds. The price for this was a very high noise level at burst speed. This didn't actually matter in combat, as the sub could outrun and evade any torpedos available at the time, but cruise speed was limited to 22-25 knots. At this speed the noise level was comparable to other Soviet and US submarines.

These boats were never actually used in combat and didn't perform any important tasks except power demonstration, but the Soviet government made use of high characteristics, exaggerating the planned vessels number. The US replied to Alfa 12 years later, by SSN-21 Seawolf, which still was less capable in an underwater dogfight, but was a little quiter at it's cruise speed. Some parity was reached with ADCAP torpedos were introduced, which are faster than Alfa-class submarines. However, Seawolf class submarines are three times heavier, don't have the Alfa's characteristic automatization and cost over 2 billions each, therefore being a very costly response to an iniative that didn't actually go beyond experiments. Their construction was halted when the last 705K submarines were decommissioned.

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Decommissioning

The first vessel was decommissioned in 1987 and four more before the end of 1992. The final vessel underwent a refit and was loaded with a VM-4 pressurised-water reactor as Project 671; after being used for training she was decommissioned in 1995.

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