The crew on Apollo 13 got back to Earth by transferring to the Lunar Module. The Lunar Module was a lifeboat for Apollo 13, and it was designed to hold two people.
All three crew members found space inside the Lunar Module before detaching it from the Service Module. Though the Lunar Module only had enough oxygen and consumables for two people to last 45 hours, the crew rationed everything in order to make it last. After the Lunar Module fully recharged the Command Module, the crew returned to the Command and unhooked before descending back to Earth landing 1 mile from the projected point.