Which submarine class is the largest ever built, measured by displacement?

The Typhoon class is the largest submarine class ever built by displacement.

The Soviet Union designed these nuclear-powered ballistic-missile submarines during the Cold War. Their immense size allowed them to carry twenty R-39 Rif missiles and to provide crew spaces, machinery and endurance suitable for long patrols beneath Arctic ice.

A Typhoon-class boat had a submerged displacement of roughly 48,000 tonnes. Its unusual design used multiple pressure hulls inside a broad outer hull, producing a distinctive, wide silhouette unlike most conventional submarines.

Six boats were constructed, although only one, Dmitriy Donskoi, remained in service into the twenty-first century before being retired. The class is sometimes confused with the smaller but heavily armed Oscar class, which was designed mainly for anti-ship warfare.