Bathysphere

From BioShock Wiki

First Bathysphere the player encounters in the game.

Andrew Ryan closed off all access to the bathyspheres during the events of the Civil War.

The Bathyspheres of Rapture are very small, comfortable submarines, allowing travel between Rapture's different zones. They were part of the city's transportation network, the Rapture Metro, created by Anton Kinkaide.

As Rapture started to break down, Andrew Ryan prohibited the use of bathyspheres by anyone outside of his inner circle. The people protested at the bathysphere station that linked the bathyspheres to Rapture and demanded to be allowed out. Obviously their demands were not met. Throughout the story, the bathyspheres are used by Jack as a mode of transportation to travel around Rapture and its "abandoned" city sections. Jack can use the bathyspheres, however, because his genetic signature is close enough to Ryan's that the security system doesn't deny him access, as Sullivan points out in one of his audio diaries. "Sisters, cousins—anyone in the ballpark genetically will be able to come and go as they see fit."