K-162, later renamed K-222, reached about 44.7 knots, making it the fastest submarine ever recorded.
The Soviet Navy built the boat as Project 661 Anchar, a high-speed nuclear-powered attack submarine. It used a titanium hull and powerful reactors, materials and machinery selected to support exceptional underwater performance. The submarine was launched in 1968 and entered service in 1971.
Its design was technically impressive but expensive and difficult to build. K-162 was the only completed boat of its class, so it did not become the foundation of a large submarine fleet. High speed also brought significant machinery noise, which could make stealth more difficult.
The boat was renamed K-222 in 1978 and remained in service until 1988. Published speed figures vary slightly because sources may distinguish between trial speed, officially recorded speed and rounded estimates, but approximately 44.7 knots is the standard headline figure.