An aqualung, also called a scuba (self-contained underwater
breathing apparatus), is a device that allows divers to breathe and move about
freely underwater for extended periods. It consists of a mouthpiece, a connecting
tube, a valve, and at least one compressed-air cylinder. The key component
is the demand valve which allows the diver to breathe air
at the pressure prevailing in the surrounding
water however great the pressure in the supply cylinder. Used air is vented
into the water. Other equipment used for scuba diving includes a wet suit
to insulate the diver from the cold, weighted belt, face mask, and flippers.
Professional divers use scuba to inspect vessels below the waterline and
to search underwater. The aqualung was invented by Jacques Cousteau and Émile Gagnan in 1943.