Project 705 Lira / Alfa class - Western Response
In 1969 strollers walking along the Neva River saw a modern-looking, small submarine tied up at the fitting-out quay at Leningrad’s old Sudomekh Submarine Shipyard. Further fitting-out activity soon convinced at least one senior submarine analyst, Herb Lord, that this submarine was an SSN, a nuclear-powered attack submarine. Western analysts noticed something they had never seen before, a “highly reflective” pressure hull section near the ALFA assembly area.
Lord subsequently conducted what is generally known as “look-back” analysis. All reports of “highly reflective” submarine hull sections at the two construction sites were collated, reviewed, and once again evaluated. It was a formidable, time consuming task. There were reports of changes to the external appearance of the assembly halls; reports dealing with unusual submarine parts at storage sites near the halls; and reports on unusual railroad cars, tank cars, and increased production of titanium sponge.
CIA had as early as 1971 published analysis — Use of Titanium by the Soviet Shipbuilding Industry — that strongly supported the assessment that the otherwise conservative Soviets had conducted serious, long-time research on shaping and welding heavy titanium plates, and that they had in fact developed that capability. Except for stainless steel — steel turns a dark, almost black color when exposed to the elements for extended periods.
A fair number of HUMINT reports dating from the time ALFA was under construction alluded to a new submarine with a small crew. Some reports cited a crew of 15, and others indicated a crew of 18 to 45. Admiral Rickover’s team believed that it was impossible to operate a nuclear submarine with such a small crew, and that it was irresponsible to automate the many vital control functions of a submarine. As a result, this information was temporarily shelved.
Since the submarine could operate at the depth of 2,200 feet — far deeper than any NATO submarine of the time, or today — it allowed the Lira to evade most contemporary NATO torpedoes. Although the Soviet boat carried a relatively small weapons arsenal, it still could wreak havoc on a NATO group without the means to effectively respond.
Construction of the first Project 661 prototype unit began around 1965, and was completed at the Sudomekh shipyard in Leningrad in 1972. Made from titanium alloys, it could accelerate to a speed of 44.7 knots, a record which will hardly be beaten in the near future.
Although a much-feared design in the West, these concerns were prompted by grossly exaggerated accounts of the boat's capabilities and an assumption that they represented the main thrust of Soviet submarine development. Any assessment of the American response to this Soviet challenge is complicated by the fact that the fast, deep-diving nuclear submarine threat proved in many ways to be a false alarm. Certainly Alfa was fast, demonstrating a 41-knot speed, but her titanium hull had actually been used to decrease displacement rather than increase operating depth, which some wester sources said was more like 1,100 feet, rather than 2,200 feet.
The fast, deep diving nuclear submarine threat proved a false alarm, but they provoked massive investments in ASW weapons by the US Navy. Steady improvements in the Mk. 48 were made, first with the Mk. 48–3 in the late 1970s, which gave the submarine a track-via-torpedo capability through the guidance wire, and then with the envelope extension program deployed in the early 1980s with a deeper operating depth, and finally with a series of ADCAP (Advanced Capability) modifications beginning in the late 1980s that apparently culminated in a 63-knot torpedo.
Tom Clancy in his highly featured the Project 705 in his book, "The Hunt for 'Red October".
Extremely noisy at high speeds, the noise levels of the Alfa at lower speeds were generally similar to that of other Soviet SSNs. The Best Depth for a submarine to avoid detection by a hull-mounted sonar is conventionally regarded as the Sonic Layer Depth plus 100 meters. This assumption is based on the premise that maximum downward refraction of sonic energy will occur at the depth of the strongest minimum sound speed gradient, thus causing short horizontal sonar ranges.
Passive acoustic-based ASW methods grew out of discoveries about low-frequency sound propagation in the sea made during and immediately after World War II. One key discovery, made by Maurice Ewing and J. Lamar Worzel, was of a deep sound channel that trapped and focused low-frequency sound, allowing it to propagate over great distances. The deep sound channel is a region in the water column in which sound velocity reaches a minimum value. Above this region, sound rays are bent downward, below it, they are bent upward; the sound rays are consequently channeled into this region. Sound traveling in this channel can be detected thousands of miles from the sound source. The so-called SOFAR (SOund Fixing And Ranging) channel was first used as a means of locating downed aviators at sea, then as a missile impact location system, but its most important application came in the form of SOSUS (SOund SUrveillance System), the network of seabed listening arrays deployed by the Navy to listen for submarines in the deep.
Cavitation noise is produced from the motion of turning propellers on surface vessels, submarines or a torpedoes. Cavitation is the formation of partial vacuums in a flowing liquid as a result of the separation of its parts. The loudest noise from normal ship operation comes from cavitation of the propeller, which adds 10-15 dBA to the noise level of regular operation. The Alfa would dive deeper in order to reduce caviation noise at high speed. The faster the Alfa moved, the deeper it had to go to avoid cavitation, deep into the deep sound channel.
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