Summary and key points you need to know: The Soviet Union’s Project 705 lira (NATO: Alfa) submarines, introduced in 1971, were groundbreaking due to their titanium hulls and lead-bismuth cooled reactors.

-These innovations enabled the Alfa-Class reach exceptional speeds of over 40 knots and dive to a depth of 350 meters, with a diving depth of 1,300 meters.

-Designed during the Cold War as a competitor to American submarines, Alfa The class was characterized by a double hull design, minimal crew requirements and impressive capabilities.

-However, initial problems with cracks in the hull were eventually resolved. Despite their advanced design, only seven ships were built and the last one was decommissioned in 1996.

The Soviet Alfa-Class submarines: speed demons of the Cold War

The modern submarine is a highly sophisticated machine that must meet demanding mechanical requirements. The requirements are demanding because the mission profile is rather unnatural.

Submarines must accommodate a crew of sailors for extended periods of time above and below sea level.

At sea, submarines are often entrusted with secret and highly sensitive operations. And the submarine must always be able to direct its various weapon systems (including nuclear weapons) at targets on land and/or at sea. The mechanical requirements for submarines are accordingly demanding.

Of course, submarine manufacturers have spent the last century innovating, pushing forward technological progress and trying to improve their machines and their fighting capabilities.

Incentive for innovation

In the 1970s, the Soviet Union was engaged in a global Cold War with the United States. The two countries vied to develop and deploy the most advanced weapons. The most obvious arena of the technology race between the two Cold War powers was, of course, space. The competition to be first, known as the Space Race, drove intense technology development – culminating in the American Apollo program and the moon landing.

But at the same time, Cold War competition was also raging in other, less visible areas. In aerospace development, for example, Soviet manufacturers such as Mikoyan and Sukhoi competed with American manufacturers such as Boeing and Lockheed to produce the most modern fourth- and later fifth-generation combat aircraft. The competition also extended to tanks, intercontinental missiles, aircraft carriers and submarines.

In order to give the Americans a certain advantage, the Soviets experimented and pushed ahead. The result was, in one case, quite novel: the construction of a submarine hull made of titanium.

Titanium hull Alfa class

In 1971, the Soviets unveiled their submarine Project 705 Lira (NATO code name Alfa). Project 705 was a nuclear-powered attack submarine that was notable for two things: the use of a titanium hull and because it was one of the fastest military submarines ever built. I

In fact, the Alfa class was inferior in speed to only one other submarine model, a Soviet prototype called the K-222.

Project 705 Lira was the first time that titanium was used in a submarine’s hull. Titanium is a chemical element that can be reduced to produce a shiny transition metal with valuable properties: low density, high strength, and resistance to seawater. Given titanium’s properties, the Soviets were understandably keen to experiment with the material in their submarine design.

Although Project 705 did not set sail until 1971, the idea was first proposed in 1957. The project was designed to meet a number of demanding requirements (under the pretext of wanting to compete with American submarine design).

The requirements were that the new submarine had to be fast enough to pursue any ship; that it had to be able to evade anti-submarine weapons; that it had to be successful in underwater combat; that it had to be difficult to detect; that its displacement had to be minimal and that the crew had to be as small as possible.

To meet the variety of requirements proposed, a titanium alloy hull was selected. The idea is that a titanium hull would provide low drag and light weight, allowing high speeds and deep dives. The design was intended to serve as an interceptor that would stay in a harbor or on a patrol route and then head toward an enemy if necessary.

The Alfa-class hull was designed as a double-hull, like most Soviet nuclear submarines. In the double-hull design, the inner hull is designed to withstand water pressure during deep dives, while the outer hull protects the inner hull and provides a more ideal hydrodynamic shape.

Like so many new technologies, the titanium hull proved difficult at first. The lightweight alloy was prone to cracking—and the first Project 705 submarine was taken out of service because of cracks in the hull. But the Soviets were able to improve their metallurgy and welding technologies to the point that all future Project 705 submarines were free of hull cracks.

To power the titanium-equipped Project 705, a lead-bismuth-cooled, beryllium-moderated reactor was installed. The liquid metal-cooled reactor had several advantages, including: greater energy efficiency; never required refueling; lighter and smaller than water-cooled reactors. The lead-bismuth-cooled reactor and its weight and power advantages were a conceptual fit with the titanium hull – both of which were geared toward building a smaller, faster ship.

The finished product was an 81-meter-long submarine with a beam of 9.5 meters and a draft of 7.6 meters. Project 705 displaced 2,300 tons when surfaced and 3,200 tons when submerged. The submarine could regularly operate at depths of 350 meters, with a diving depth of about 1,300 meters. Most impressively, Project 705 could reach speeds in excess of 40 knots – all while carrying a crew of torpedoes and/or cruise missiles and/or mines.

A total of seven Alfa-class submarines of Project 705 were commissioned, one of which remained in service until 1996.

About the author: Harrison Kass

Harrison Kass is a prolific defense attorney who has published over 1,000 articles. Harrison is a lawyer, pilot, guitarist, and professional hockey player. He joined the U.S. Air Force as a student pilot but was medically discharged. Harrison has a BA from Lake Forest College, a JD from the University of Oregon, and an MA from New York University. Harrison listens to Dokken.

All images are Creative Commons. The image shows an Akula-class submarine.