Submersibles are constructed in a variety of sizes and shapes and are designed to perform different and often highly specialized tasks. The inherent danger in a bathysphere was its inability to surface on its own accord, being raised and lowered by a winch system on a surface vessel. In 1954 one of the first types of submersible, the bathyscaphe, was designed and successfully tested by the Belgian scientist Auguste Piccard to overcome this problem and to provide limited maneuverability. A bathyscaphe is in effect an underwater balloon. The cabin is suspended beneath a large flotation chamber that contains gasoline and iron pellets.
Submersion is accomplished by release of some gasoline, rendering the craft heavier than water.
To rise, some of the iron-shot ballast is released. The Alvin was also used to photograph and retrieve objects from the Titanic after its discovery in 1987. The Columbia Encyclopedia, Sixth Edition.