An underwater breathing apparatus is a device used to allow a person to breathe underwater. The most common types of underwater breathing apparatus are the AQUALUNG, snorkel, GILL, and scuba. An AQUALUNG is a self-contained underwater breathing apparatus that consists of a tank of compressed air and a regulator to control the flow of air. A snorkel is a tube that extends from the surface of the water to the user's mouth, allowing them to breathe without having to come up for air. A GILL is a device that mimics the function of a fish's gills, allowing the user to extract oxygen from the water. Finally, a scuba is a self-contained underwater breathing apparatus that uses a tank of compressed air and a regulator to control the flow of air.