The bathysphere was the first modern system designed for the purpose of deep-sea exploration. Developed by American naturalist William Beebe and engineer Otis Barton in the early 1930s, it consisted of a steel sphere with windows of fused quartz and equipped with searchlights, an oxygen supply, and a telephone. The sphere had to be lowered and raised by cable from a ship, and no rescue was possible if the cable broke. The deepest descent made by Beebe and Barton, in 1934, was to 923 m (3,028 ft). Later versions of the bathysphere have been called benthoscopes.