The ancient Greeks practiced commercial and military diving, usually with little or no equipment. In the Iliad, Homer describes the use of divers in the Trojan Wars; Greek laws regulating those who dived for sunken treasure are found as early as the 3d cent. B.C. Before the introduction of modern apparatus, divers submerged with the aid of a rope and a stone weight; using the rope as a guide for position, the naked diver quickly scooped up whatever commodity was being sought.
Inventors as early as the 17th cent. sought means whereby divers could stay underwater for extended periods. At that time, various types of diving dress and underwater armor attempted to supply fresh air through a surface pipe kept above the water by a float. Augustus Siebe devised the first practical diving equipment early in the 19th cent. in England. His first suit was of the open type, consisting of a helmet attached to a jacket made of waterproof material. Air was pumped to the helmet through a pipe from the surface—air pressure serving to keep the water level below the diver's head and the air finally escaping through open vents at the bottom of the jacket. The diver had to maintain a generally upright position; a fall could result in drowning because the air in the suit was likely to rush out through the vents. To correct this difficulty, Siebe later developed the closed type of diving suit that, with improvements, is still in general use. Instead of the earlier open vents, the closed type of suit had valves that let air out without letting water in, regardless of the diver's position. The limitations imposed on the helmet diver's lateral movement (because of the connection to the surface) led to early interest in alternative equipment that would permit freer movement, but the scuba apparatus was not developed by Jacques Yves Cousteau and Emil Gagnan until well into the 20th cent. In 1943 successful tests were made of the new compressed-air breathing apparatus, and it has been widely used since.
Several types of large metallic structures have been used as underwater diving vessels since early times. Aristotle, as early as 360 B.C., mentions sponge divers using primitive vessels. Otis Barton's bathysphere—a hollow, globular steel structure built to withstand tremendous pressure—was used in undersea exploration in the 1930s, but an attached steel cable and winch limited its mobility. The first free and self-contained diving craft was Auguste Piccard's bathyscaphe. His craft, the Trieste, descended (1960) to 35,000 ft (10,668 m), the deepest known point in the ocean.