The cargo bay doors of an Andorian battle cruiser
The cargo bay doors, cargo bay hatch, cargo hatch, payload bay doors, or simply bay doors, were the access points for cargo to enter or depart a starship or space station's cargo bay.
Following the return of the HMS Bounty to 23rd century Earth after returning from 1986 to return a pair of humpback whales from the past, the Klingon Bird-of-Prey crash landed in San Francisco Bay. As the Bird-of-Prey began to sink, the whales became trapped in the ship's cargo bay when the bay doors lost power. When Rear Admiral James T. Kirk suggested to Commander Montgomery Scott to use the explosive override, Scott informed them that it was under water and there was no way to reach it. Kirk, however, was successfully able to swim to the control and opened the bay doors to allow the whales to escape. (Star Trek IV: The Voyage Home)