Why the fastest-warship question has several answers

What was the fastest warship ever built?

Probably either a U.S. carrier or a nuclear submarine, with Soviet Akula- and Papa-class boats mentioned as candidates depending on whether raw speed or speed plus power is emphasized.

The candidates divide between a U.S. aircraft carrier and a nuclear submarine, so one surface-versus-underwater comparison cannot settle the question. The Akula class is mentioned as a submarine candidate. A follow-up selects the Papa class when speed is considered together with power and notes the unusual materials used in fast Soviet submarine designs. The discussion does not claim access to a definitive trials table or classified maximum figure. Any answer must distinguish platform category, raw speed, available power, and construction choices.