The first recorded submersible was reportedly a primitive diving bell, probably made of wood, in which the ancient Greek leader and general Alexander the Great (356-323 bc) was briefly lowered into the Mediterranean Sea. Diving bells are small, dome-shaped chambers that hold a limited amount of air. They are still occasionally used by divers. The modern era of submersibles began with the American ocean scientist Charles William Beebe in 1930. Along with American engineer Otis Barton, Beebe pioneered the use of a tethered, manned submersible, which he named the bathysphere. It was a spherical metal ball, constructed of steel, with two viewing windows, and was able to withstand the high pressure of undersea exploration. Beebe and Barton reached a depth of 435 m (1,427 ft) in 1930, and a depth of 923 m (3,028 ft) in 1934.
Swiss physicist Auguste Piccard created the second generation of deep-diving exploration vehicles. An acquaintance of Beebe, Piccard was a reputable inventor who had devised a number of designing instruments for Albert Einstein. In 1947 Piccard designed a bathysphere-type hull for a human crew, but added a massive buoyancy tank filled with lighter-than-water gasoline. Piccard called the submersible the bathyscaphe. Lead pellets and tanks filled with water provided the necessary weight to sink the craft. To resurface, the pellets were released and the water expelled, enabling the vehicle to surface without being tethered to a host ship. Using the bathyscaphe, Piccard reached a depth of 4,000 m (13,125 ft).
A bathyscaphe took Jacques Piccard and Donald Walsh to the deepest spot in the ocean in 1960. The long visible tank is filled with gasoline for buoyancy. Entrance to the small pressurized chamber underneath is made through the tower in the middle of the bathyscaphe.
In 1958 the Navy purchased Piccard’s deep-diving submersible and assigned it to a research unit that handled other Navy submersibles, such as the DSRV rescue submersibles. Jacques Piccard, Auguste Piccard’s son, worked with the Navy unit. On January 23, 1960, he and Navy Lieutenant Don Walsh descended to a record depth of 10,915 m (35,810 ft) in the bathyscaphe Trieste. The dive took place in the Pacific Ocean in the Challenger Deep, which is located in a deep depression known as the Mariana Trench on the ocean floor. The Challenger Deep is the deepest place on the earth. At that depth, Trieste withstood pressures as high as 1.17 metric tons/sq cm.
From the 1950s to the 1980s the U.S. Navy led the way in deep-ocean exploration. The Navy was motivated by the need to track Soviet submarines and to improve underwater navigation and antisubmarine warfare tactics. The Navy’s efforts accelerated after a malfunction caused the loss of the submarine USS Thresher during a 1963 test run. After the accident, the Navy developed deep-sea rescue vehicles that could descend and dock with damaged submarines. The Navy has also used its deep-sea technology for other purposes. After the fall of the USSR in 1991, the United States revealed a number of secret missions carried out by its submarines. One operation, code-named Ivy Bells, used submarines and submersibles to install a listening device on an underwater Soviet communications cable in the Sea of Okhotsk.
As international tensions subsided in the 1980s, civilian researchers gained access to the Navy's fleet of submersibles for a number of scientific and archaeological expeditions. One of the most famous expeditions was the 1986 discovery and survey of the Titanic in the North Atlantic. Popular interest in oceanographic exploration was also enhanced by the work of French explorer Jacques-Yves Cousteau, who is credited with the invention of the aqualung, an underwater breathing device (also referred to as scuba gear). Cousteau built a number of small piloted submersibles capable of shallow-water dives.
A growing civilian industry has adapted the Navy’s once-classified machinery and techniques for commercial uses. ROVs were first used to locate Navy submarine wrecks, but are now used by commercial and scientific groups. ROVs, alongside human divers, were used to salvage debris from Trans World Airlines Flight 800, which crashed off Long Island, New York, in 1996. The latest submersibles in development are robotic vehicles called autonomous underwater vehicles, or AUVs. These untethered craft are designed to operate individually according to a preprogrammed set of instructions. This preprogramming allows AUVs to perform simple routine tasks without the need for people to control them. Possible uses for AUVs include the periodic monitoring of seabeds for changes in biological growth and the provision of security for underwater areas.