USS Nautilus (SSN-571) in the context of "Nuclear-powered submarine"

A submarine (often shortened to sub) is a watercraft capable of independent operation underwater. (It differs from a submersible, which has more limited underwater capability.) The term "submarine" is also sometimes used historically or informally to refer to remotely operated vehicles and robots, or to medium-sized or smaller vessels (such as the midget submarine and the wet sub). Submarines are referred to as boats rather than ships regardless of their size.

Although experimental submarines had been built earlier, submarine design took off during the 19th century, and submarines were adopted by several navies. They were first used widely during World War I (1914–1918), and are now used in many navies, large and small. Their military uses include: attacking enemy surface ships (merchant and military) or other submarines; aircraft carrier protection; blockade running; nuclear deterrence; stealth operations in denied areas when gathering intelligence and doing reconnaissance; denying or influencing enemy movements; conventional land attacks (for example, launching a cruise missile); and covert insertion of frogmen or special forces. Their civilian uses include: marine science; salvage; exploration; and facility inspection and maintenance. Submarines can be modified for specialized functions such as search-and-rescue missions and undersea cable repair. They are also used in the tourism industry and in undersea archaeology. Modern deep-diving submarines derive from the bathyscaphe, which evolved from the diving bell.

Chester William Nimitz (/ˈnɪmɪts/; 24 February 1885 – 20 February 1966) was a fleet admiral in the United States Navy. He played a major role in the naval history of World War II as Commander in Chief, US Pacific Fleet, and Commander in Chief, Pacific Ocean Areas, commanding Allied air, land, and sea forces during World War II.

Nimitz was the leading U.S. Navy authority on submarines. Qualified in submarines during his early years, Nimitz later oversaw the conversion of these vessels' propulsion from gasoline to diesel, and then later was key in acquiring approval to build the world's first nuclear-powered submarine, USS Nautilus, whose propulsion system later completely superseded diesel-powered submarines in the United States. Beginning in 1917, Nimitz was the Navy's leading developer of underway replenishment techniques, the tool which during the Pacific war would allow the American fleet to operate away from port almost indefinitely. The chief of the Navy's Bureau of Navigation from 1939 to 1942, Nimitz served as the Chief of Naval Operations from 1945 until 1947. He was the United States' last surviving officer who served in the rank of fleet admiral. The USS Nimitz supercarrier, the lead ship of her class, is named after Nimitz.

The Naval History and Heritage Command, formerly the Naval Historical Center, is an Echelon II command responsible for the preservation, analysis, and dissemination of U.S. naval history and heritage located at the historic Washington Navy Yard. The NHHC is composed of 42 facilities in 13 geographic locations including the Navy Department Library, 10 museums and 1 heritage center, USS Constitution repair facility and detachment, and historic ship ex-USS Nautilus.

Idaho National Laboratory (INL) is one of the national laboratories of the United States Department of Energy and is managed by the Battelle Memorial Institute. Historically, the lab has been involved with nuclear research, although the laboratory does other research as well. Much of the current knowledge of nuclear reactor behavior was discovered at what is now Idaho National Laboratory. John Grossenbacher, a former INL director, said, "The history of nuclear energy for peaceful application has principally been written in Idaho". The present facility resulted from the 2005 merger of two neighboring laboratories, the National Engineering and Environmental Laboratory, and the Idaho site of the western branch of Argonne National Laboratory (Argonne-West).

Various organizations have built more than 50 reactors at what is commonly called "the Site", including the ones that gave the world its first usable amount of electricity from nuclear power and the power plant for the world's first nuclear submarine. Although many are now decommissioned, these facilities are the largest concentration of reactors in the world.