What do the crew call the Klingon ship they steal in Star Trek IV?

The crew call the Klingon ship they steal in Star Trek IV the HMS Bounty. After the USS Enterprise is destroyed in Star Trek III, Admiral Kirk and his crew travel back to 20th-century Earth aboard a captured Klingon Bird of Prey.

The name is a playful reference to the historical HMS Bounty, the British vessel associated with the 1789 mutiny led by Fletcher Christian against Lieutenant William Bligh. In the film, Kirk's crew similarly takes control of a ship that originally belonged to another crew, making the name an intentional historical joke.

The vessel is technically a Klingon Bird of Prey rather than a British ship, and its Klingon designation is not generally used by the crew. That is why answers such as USS Reliant, HMS Victory, and USS Enterprise do not fit. The Bounty remains the crew's transport through most of the film and is later used to rescue Earth by creating a powerful gravitational slingshot around the sun.