Developed by French physicist Auguste Piccard and his son Jacques, the bathyscaph Trieste was a scientific marvel that allowed unprecedented scientific, technical, and military feats in the ocean depths. France and the United States both acquired and subsequently developed variants of the original bathyscaph. While both France and the United States employed the bathyscaph as a tool for scientific investigation of the deepest ocean depths, the U.S. Navy developed and employed the Trieste for military missions as well. From its earliest years, participants in the Trieste program realized that they were making history, blazing a trail into previously unexplored and unexploited depths, developing new capabilities and opening a new frontier. Comparisons with developments in space and the space-race between the United States and the Soviet Union often were made concerning the Trieste program and contemporary developments in undersea technologies and capabilities. The Trieste opened the entire oceans to exploration, exploitation, and operations. The bathyscaph was a first-generation system, a Model-T that spawned an entirely new industry and encouraged new concepts for deep-ocean naval operations. Advances in deep-sea technologies lacked the gee-whiz factor of the concurrent space race, but were highly significant in the development of new technology, new knowledge, and new military capabilities. Opening the Great Depths is the story of the three Trieste deep-ocean vehicles, their officers and enlisted men, and the civilians, often told in their own words, documenting for the first time the earliest years of humanity's probing into Earth's final frontier.