Built and designed over 50 years ago, the Soviet K-222 submarine still holds the record for the world’s fastest submarine ever built, reaching speeds of 82.8 kilometers (51.4 miles) per hour or 44.7 knots.

Initially known as K-162, the K-222 was developed under the orders of the Central Committee of the Communist Party of the Soviet Union and the country’s Council of Ministers in 1958 as part of an effort to engineer a “new high-speed submarine”. Constructed in the northern port city of Severodvinsk through the 1960s, a single sub from so-called Project 661 was commissioned in 1969.

Nuclear-armed and nuclear-powered, the sub measured just over 106 meters (347 feet) in length and was one of the first submarines to have a titanium hull. Clearly, though, speed was its stand-out feature. 

Upon being tested in 1969, it proved to be even faster than they’d hoped, reaching speeds of 42 knots rather than 38. It reached its peak during a 1971 test in which it achieved 44.7 knots at full reactor power, a submarine speed that hasn’t been topped since. 

It might sound like the K-222 posed a formidable threat to the US and other NATO forces of the Cold War, even if the challenge was merely to their pride and technological prowess. By comparison, one of the fastest subs ever developed by the US is the nuclear-propelled attack submarine Seawolf, which reaches speeds of 35 knots or 64 kilometers (40 miles) per hour.

However, its whizzing power made it a difficult beast to tame. The high speeds caused structural stress, plus the system proved to be very complicated and expensive to run. Inside the submarine’s control room, the noise could reach levels of 100 decibels, almost as loud as a bustling nightclub. 

A decisive blow to the project came in September 1980 when an incident occurred during the maintenance of its nuclear reactor. It was eventually decommissioned in 1988 before being scrapped in 2010.

Given the engineering difficulties highlighted by the K-222, it’s hard to imagine any submarine will ever beat its speed record – although anything is possible.