Nuclear powered submarines with titanium hulls were a big achievement of the Soviet Union’s shipbuilding industry. The navies of other countries have no such submarines. Designing and building them pursued the goal of reaching technological and tactical superiority in comparison with the submarines of potential adversaries.
Soon after commissioning of the first Soviet attack nuclear submarine (Project 627), on August 18, 1948, the Decree of the Soviet Government was issued. “About creation of a new high speed submarine, new types of power plants and research and development for submarines.” In accordance with that decree, works began on a new high speed nuclear submarine with anti-ship cruise missiles launched underwater and a hull from titanium alloys (Project 661-Papa).
The submarine was laid down in Severodvinsk in December 1963 and commissioned in December 1969. She had four 433 mm torpedo tubes with 12 torpedoes, and 10 Ametist 1600 mm missile tubes. The range of Ametist was up to 60 km.
With two reactors, two turbines, and two propellers in a nuclear power plant of 80,000 hp, the submarine (surfaced displacement 5200 tons) reached a speed of 44. 7 knots.
Her test depth of 400 meters (m) (100 m more than Project 627) was provided by using titanium alloy 48-OT3B with a specific weight of 4.5 gram/cubic centimeter and a yield of 6000 kg/square centimeter.
For building the project 661 submarine a new metallurgical branch was created for production of plates and profiles from titanium and also of forging and stamping from that material.
The Severodvinsk shipyard gained experience with titanium hull welding and the production of castings and frameworks. To work with titanium hulls special shops had been built. Static, cyclic and dynamic tests of titanium structures showed high qualities including blast resistance.
The Project 661 submarine was built in December 1969, but due to high cost and too long a building process, serial production did not take place.
The first serial production of a titanium nuclear submarine became Project 705-Alfa.
She was built in Leningrad and commissioned in December 1971. During the period of 1972-1982 two more submarines were built in Leningrad and three in Severodvinsk.
With a surfaced displacement of 2300 tons, a test depth of 400 m, six 533 mm torpedo tubes (18 torpedoes and anti-submarine missiles), one reactor and one turbine power plant (40,000 hp) and a complement of 25-30 submariners, she reached 42 knots. The serious deficiency of that submarine appeared in her reactor with a liquid Pb-Bi heat carrier which was unreliable and difficult to maintain in fleet conditions.
The same titanium alloy played its role in reduction of her displacement and increase in her diving depth.
The full implementation of titanium advantages took place on the nuclear submarine KOMSOMOLETS (Project 685) which was designed in Leningrad from 1966 and built in Severodvinsk in 1978-1983.
Using a titanium alloy with a yield strength of 7200-7500 kg/square centimeter, allowed a test depth of 1000 meters with her hull weight about 39 percent of the surfaced displacement. One reactor, one turbine nuclear power plant (40,000 hp) provided a speed of more than 30 knots. The submarine had six 533 mm torpedo tubes (28 torpedoes or anti-submarine missiles). Unfortunately she was lost in the Barents Sea in 1994 as a result of fire in the seventh compartment. Serial production of titanium attack nuclear submarines was also attained with Project 945; the Sierra class submarine on which the author of this article was Chief Navy Supervisor.
For building of these submarines, Krasnoe Sormovo’s (Nizhny Novgorod) internal shipyard was chosen and that factor put a strict limitation on her displacement. The Sormovo’s Design Bureau Lasurit (Chief Designer Nikolay Kvasha) designed that submarine.
The most important differences between Project 945 (Sierra) submarine and the previous Project 671 (Victor) submarines were increases in her weapons payload and in test depth (up to 40 torpedoes and/or anti-submarine missiles and 600 m test depth).
Titanium alloy 48-0T3V (yield strength 6000 kg/square centimeter) provided the possibility to reduce the hull weight (and thus displacement) of this submarine by more than 10 percent in comparison with a relevant steel submarine.
Other positive qualities of titanium alloys were:
- corrosion steadfastness (endurance) in sea conditions
- more possibilities to increase yield point in comparison with steels.
At first it was planned to build a series of about 40 units of that class of submarines. They had to be built in two shipyards: Krasnoe Sormovo and Sevemoe Mashinostroitelnoe Predpriyatie in Severodvinsk. But ultimately only four submarines were built in Sormovo and were commissioned to the North Fleet in 1984-1993. The Project 945 Sierra class submarines has the following characteristics:
Purpose: blue water anti-submarine and anti-ship operations
Surfaced displacement 6,000 tons
Submerged displacement 10,000 tons
Reserve buoyancy 29 percent’s
Surface unsinkability with one flooded compartment
Length 107 m
Beam 12 m
Draft 8.5 m
Test Depth 600 m
Collapse depth 840 m
Submerged speed 35.5 knots
Torpedo/missile tubes, bow 4-650 mm and 4-533 mm
Weapons 12-650 mm and 28-533 mm torpedoes and ASW missiles
Sonars/fire control: SCAT and BICS
Reactor: one OK-650, 190 mgwt
Turbine: one 50,000 shp
Manning: approximately 60 (30 officers and 30 petty officers)
In spite of the above mentioned advantages of the third generation Soviet titanium attack nuclear submarines, submarine development went back to the building of steel submarines with Project 974-Akula. (Design Bureau Malachite in St. Petersburg, Chief Designer Georgy Tchernyshov, Chief Naval Supervisor Igor Bogachenko) construction was in the Komsomolsk and Severodvinsk shipyards.
The main reason in favor of steel was lower cost and more developed technological process.
The negative consequences of the return to steel were an increase in Akula’s surfaced displacement up to 8000 tons and submerged displacement up to 13000 tons and reduction of her speed to 33.0 knots. Positive changes were the introduction of anti-land cruise missiles and more sophisticated hydroacoustic/weapons control systems. Her hull material was steel AK-32 with a yield strength of 10,000 kg/square centimeter.
From 1984 to 1996, 14 Project 971 submarines were built (seven for the Pacific Fleet in the Komsomolsk on Amur shipyard and seven for the Northern Fleet in the Severodvinsk shipyard).
In conclusion, it is reasonable to return to the advantages of titanium as a submarine hull material. The author of this article continues to consider it as a superior potential option.
The number one titanium advantage is the so-called specific strength: the ratio between yield strength in kg/sq mm and specific weight in g/cubic cm. They are:
1960s -1970s 1980s-1990s
80/7.8==10.3 100/7.8= 12.8
60/4.45= 13 72/4.45= 16.0
The number two advantage is in the submarine’s magnetic properties. When a submarine is sufficiently quiet the magnetic field plays an important role in her stealthiness. If the magnetic field stress of titanium submarines is less by 8-10 times than that of steel ones, their magnetic moments are less by dozens of times. In other words, the mine threat for titanium submarines is much less and degaussing devices are much simpler.
The number three advantage is corrosion resistance. The titanium hull practically does not need repair. If one can speak figuratively, it is eternal.
A disadvantage of titanium is the higher cost of material and shipbuilding technological processes. The cost of one ton of titanium is twice that of steel. The cost of shipyard hull work is more than steel by 20-30 percent. But these ratios are for initial steps of titanium submarine building in very limited numbers. The increasing of diving depths, reduction of displacements, unmanliness and corrosion resistance makes titanium nuclear submarines more than cost effective in comparison with their steel counterparts.
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