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Limits RegistryThe Soviet Project 705 Lira (NATO reporting name 'Alfa') class attack submarines, powered by a lead-cooled fast reactor, were reportedly capable of submerged speeds of around 41 knots (76 km/h), with some trial reports citing even higher figures — widely regarded as the fastest submarines ever built, though exact top-speed figures remain only partly declassified.
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The Soviet Project 705 Lira (NATO reporting name 'Alfa') class attack submarines, powered by a lead-cooled fast reactor, were reportedly capable of submerged speeds of around 41 knots (76 km/h), with some trial reports citing even higher figures — widely regarded as the fastest submarines ever built, though exact top-speed figures remain only partly declassified.
The highest submerged speed attributed to any submarine, based on declassified and publicly reported naval performance figures.
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Limits Registry. LR-FASTEST-SUBMARINE-SPEED. Fastest submerged speed ever recorded by a submarine. 2026.