Apollo 13
The craft launched successfully toward the Moon, but two days after launch a faulty oxygen tank exploded. It damaged the Service Module. It lost oxygen and electrical power. There was a very large chance that the astronauts would die before they could return to Earth. They were very short on oxygen. Oxygen is not just used to breathe; on the Apollo spacecraft it was used in a device called a Fuel cell to generate electricity. So they saved their remaining air by turning off almost all their electrical equipment, for example heaters. It became very cold in the spacecraft.