Klingon Bird-of-Prey captured by Kirk from Commander Kruge in 2285 and used to travel back in time to save Earth from the whale probe.
The Bounty began as the Bird-of-Prey of Commander Kruge, a Klingon officer who came to the Genesis Planet to seize the secrets of the Genesis Project. Small, fast and equipped with a cloaking device, it was typical of the Klingon raiders of its day.
In Star Trek III: The Search for Spock, Kruge's ship destroyed the USS Grissom and crippled the Enterprise. Kirk lured a Klingon boarding party onto the Enterprise and set it to self-destruct, then defeated Kruge on the disintegrating planet and captured the Bird-of-Prey, using it to carry the revived Spock to Vulcan. During the crew's exile there, McCoy named the ship the Bounty.
In Star Trek IV: The Voyage Home, Kirk flew the Bounty around the Sun to travel back to 1986, where the crew collected two humpback whales and brought them forward to answer the probe threatening Earth. The ship lost power on its return and crashed into San Francisco Bay, where it was abandoned after the whales were released.