The only Project 661 boat ever made was extremely fast underwater, but was also costly and complex to build and operate.
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Sixty years ago, Soviet engineers began developing a new submarine under strict orders to eschew previous design decisions in favor of innovative concepts wherever possible. The resulting boat, a guided missile submarine that was known first as K-162 and eventually as K-222, established a still-unbeaten underwater speed record and was the first titanium-hulled submarine ever, but also proved too expensive and complicated to be anything more than a one-off, earning the nickname "Golden Fish."
K-162/K-222, the only Project 661 submarine ever built, was the product of a direct order from the Central Committee of the Communist Party of the Soviet Union and country’s Council of Ministers on Aug. 28, 1958. The directive called for a new “high-speed submarine” and development began the following year. The Project 661 design was also known as the Anchar-class in the Soviet Union and NATO referred to it as the Papa-class, even though there was only ever one boat.
The immediate impetus for the development of the Project 661 design was the limited capabilities and poor performance of the first generation of Soviet diesel-electric guided missile submarines, or SSGs. These early boats were conversions of Whiskey-class submarines, which were themselves derived from World War II-era Nazi U-boat designs.
When work on the Project 661 submarine started, the Soviets had already separately begun development of new classes of purpose-built conventionally-powered guided missile submarines (SSGs) and nuclear-powered guided missile submarines (SSGNs), the Project 651s and Project 659s respectively, which were also known as the Juliett- and Echo-classes in the West. But the goal for the new project was to produce an entirely novel cruise missile-carrying submarine that would be even more capable than either of these interim designs.
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The Soviet Project 651 or Juliett-class guide missile submarine K-77.
The first major decision the designers made was to use titanium alloys for the submarine’s external and internal hulls rather than steel or aluminum. Titanium offered benefits in terms of its general strength and resistance to corrosion.
Though titanium is also only weakly magnetic, this did not render the Project 661 immune to detection by aircraft with magnetic anomaly detectors (MAD) or magnetic mines. This is due to the presence of more magnetic metals in the alloy, as well as various other components inside the submarine itself.
Compared to earlier Soviet submarines that still showed the influence of World War II-era designs, the hullform of the Project 661 was significantly different, featuring a rounded bow and a streamlined “split-feed” stern with twin propellers. The 1970s-era Project 949 SSGNs, or Oscar-class, would also use this same general arrangement.
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A Cold War-era photo of K-162/K-222 showing its rounded nose.
Public Domain
A still from a Soviet-era film about the Project 661 submarine showing its twin screws. The shrouds around the propellers were no longer in place when the submarine entered service.
The Soviets had never had to build such large titanium alloy components. So, while fabrication of the first components for the Project 661 submarine began in 1962, the need to devise entirely new and complex manufacturing processes meant the submarine was not officially laid down until December 1963. Years later, during construction of the titanium alloy hulled Project 705submarines, also known variously as the Lira-class or Alfa-class, workers reportedly had to craft the hull sections inside a shed filled with inert argon gas, requiring the use of cumbersome "moon suits" with their own air supply.
For the Project 661 submarine, the Soviets also developed an advanced nuclear pressure water reactor, as well as a prototype lead-bismuth eutectic(LBE) cooled design. LBE reactors have greater thermal efficiency and can operate at higher temperatures than water-cooled designs without risk of the coolant boiling off.
Unlike other liquid metal-cooled reactor types, such as sodium or sodium-potassium designs, LBE does not react spontaneously with air or water, reducing the size and complexity of the entire coolant system and eliminating the risk of an explosion in the event of a leak. Unfortunately, LBE is also much more corrosive and has a higher melting point.
This means this type of reactor typically has a shorter overall lifespan and there is a risk of the coolant solidifying if the reactor drops below a certain temperature, requiring significant power to keep it sufficiently warm at all times. Furthermore, as the coolant becomes irradiated over time, it forms highly radioactive polonium-210 – a substance dangerous enough to work as an assassination weapon – as a byproduct, making it especially hazardous to refuel the system or otherwise handle any contaminated components.
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K-162/K-222 underway.
The Soviets ultimately opted to install two highly compact VM-5 pressure water reactors, despite their lower performance. Even so, each one of them produced up to 177 megawatts of power. By comparison, the Echo-class SSGNs had a single, earlier VM-A that only generated a maximum of 70 megawatts.
The immense power from these reactors, combined with its lightweight, but strong titanium hulls, helped give the submarine a relatively blistering speed underwater. The Project 661 boat could cruise submerged at just shy of 44 miles per hour. It broke the world speed record for a submarine traveling undersea during its sea trials, reaching a maximum speed of more than 51 miles per hour.
The U.S. Navy’s Los Angeles-class nuclear-powered attack submarines, improved variants of which remain service today, have an official top speed of 23 miles per hour when submerged. There have been reports that these boats can actually get up to around 35 miles per hour underwater. The latest American Virginia-class attack submarines have a publicly stated top submerged speed of around 29 miles per hour, but this is still significantly slower than the Project 661 design.
The Soviet-era film below, though in Russian only, still offers an interesting look at K-162/K-222, its development, and the submarine in action.