Sept. 30, 1954: The World’s First Nuclear-Powered Submarine, U.S.S. Nautilus, Enters Navy Service

In the spring of 1939, Enrico Fermi met with representatives from the U.S. Navy and Army to share big news: The uranium atom had been split, opening the potential of nuclear energy for explosives and power generation.

The meeting didn’t spark an immediate bomb effort, as Enrico Fermi and his colleague Leo Szilard had hoped. It would take several months for the gears of what would become the Manhattan Project to start turning, spurred by a letter President Franklin D. Roosevelt received from Szilard and Albert Einstein in October of that year. But the meeting did spark immediate action in another direction: nuclear-powered propulsion.

For years, the U.S. Navy had been pursuing alternative energy sources for ships, particularly its submarines. Limited by their power source, the vessels could stay underwater for just 12-48 hours. Even before the meeting with Fermi, Ross Gunn, the prolific and versatile physicist in charge of the Mechanics and Electricity Division at the Naval Research Lab (NRL), had realized that theoretically, nuclear energy could revolutionize their capacity.

Gunn “was not particularly interested in the development of an atomic bomb, but he was pointedly aware of the distinct advantages of controlled nuclear power to the U. S. Navy,” wrote Carl Holmquist and Russell Greenbaum in a 1960 article for the U.S. Naval Institute’s Proceedings.

To Gunn, Fermi’s meeting signaled it was time to start experimenting.

At the time, submarines relied on electric batteries for underwater propulsion, but the batteries were charged by diesel-powered generators that required frequent resurfacing, fuel, and oxygen. The Navy had considered other propulsion sources, such as fuel cells, but oxygen remained the limiting factor. Gunn envisioned an entirely new power source — a uranium core that would heat water to run a steam power plant onboard.

Shortly after Fermi’s meeting, Gunn’s division secured funding to begin research. Step one was to enrich uranium, so the team explored ways to separate uranium isotopes. Work progressed slowly at first but picked up speed when Gunn began working with Philip Abelson, a physicist at the Carnegie Institution of Washington who had recently pioneered a method of liquid thermal diffusion to separate the isotopes.

Abelson had designed a tall, thin column from three concentric pipes. The innermost pipe held steam, the middle pipe dissolved uranium hexafluoride, and the outermost pipe cooling water. The temperature gradient experienced by the middle pipe caused the lighter uranium-235 isotopes to diffuse toward the hot inner pipe and travel upward, while the heavier uranium-238 isotopes traveled downward, said Abelson in an interview with the Atomic Heritage Foundation. “All one has to do is fill this thing and put steam in and cooling water and go away for three days, and one has some separation.”

The Bureau of Standards and NRL helped Abelson test the method on successively bigger scales — the greater the temperature gradient and taller the column, the better the output. After supporting the work for several months, Gunn hired Abelson in 1941. “For a time, the facility at the Naval Research Laboratory was the world's most successful separator of uranium isotopes,” Abelson wrote in the National Academies Biographical Memoirs. By 1944, they had a 300-column plant at the Philadelphia Naval Shipyard.

In the meantime, the U.S. Army’s Manhattan Project worked feverishly on other types of uranium enrichment but did not share any information, even with the Navy. Still, most of the shipyard’s enriched uranium went to the Manhattan Project. Submarine research stalled.

“The NRL’s efforts to develop a nuclear-powered submarine were blocked by the Manhattan Project’s monopoly on nuclear research,” wrote University of Pennsylvania archivist Joseph-James Ahern in an International Journal of Naval History paper. He reports Gunn as having recalled, “We had the hose turned on us!”

On seeing Abelson’s favorable results, the Manhattan Project built a copycat liquid thermal diffusion plant with 2,142 columns, each 15 meters tall, at Oak Ridge National Laboratory (ORNL). The so-called S-50 plant played a critical role in history. A trio of plants enriched uranium in series for the first atomic bomb, which was dropped on Hiroshima, Japan, on Aug. 6, 1945; the first feeder plant was S-50.

After World War II, Gunn received an award from the Secretary of the Navy for his “outstanding contribution to the development of the atomic bomb.” He and Abelson returned to promoting research on nuclear-powered submarines as countries became increasingly adept at detecting diesel submarines. In 1946, at Gunn’s urging, the Navy sent personnel to learn about nuclear energy from Manhattan Project scientists, now under the Atomic Energy Commission.

That same year, Abelson returned to the Carnegie Institution and transitioned to biophysics. Soon after, Gunn left NRL for the United States Weather Bureau. In their wake, a new champion for nuclear-powered submarines emerged: Captain Hyman Rickover.

Rickover, an electrical engineer, was one of five people the Navy assigned to learn about nuclear energy. He quickly grasped the benefits of nuclear power and went on to head the new Nuclear Power Branch of the Navy’s Bureau of Ships and, simultaneously, the Division of Reactor Development for the Atomic Energy Commission. With the uranium quest resolved, he led the effort to design a safe and compact power plant for a submarine.

Under Rickover, a group of engineering duty officers worked with experts such as physicist Alvin Weinberg, administrator of ORNL, and Harold Etherington, director of the Naval Reactors Division at Argonne National Laboratory, and their civilian teams to experiment with reactor designs.

“There were several reactor concepts; the real challenge was to develop this technology and transform the theoretical into the practical,” says a commemorative article released by the Naval Nuclear Propulsion Program in 2023. “New materials had to be developed, components designed, and fabrication techniques worked out.”

The team designed a pressurized water reactor, a model for the most common types of nuclear reactors, even today. Water in a coolant loop is kept under high pressure and pumped near a core of slightly enriched uranium. The water heats up, but the high pressure keeps it from boiling. The heated water then travels into a steam generator where it vaporizes water in a secondary loop. The resulting steam turns a turbine generator and creates electricity.

In the early 1950s, Rickover contracted with the manufacturing company Westinghouse to build the reactor and the Electric Boat Division of General Dynamics to build SSN-571, the submarine it would power. The submarine underwent extensive safety testing before and after the Navy installed the reactor. In addition, Rickover personally interviewed and approved every Navy member of the nuclear reactors program — not just initially, but for decades.

U.S.S. Nautilus was launched on Jan. 21, 1954, and on Sept. 30, more than 1,200 people gathered for the submarine’s commissioning. The world’s first nuclear-powered submarine raised its U.S. flag, and the vessel officially entered Navy service. After a few months of additional testing and construction, Commander Eugene P. Wilkinson ordered the lines cast off Nautilus in January 1955, and it took to sea, signaling back, “Underway on nuclear power."

Nautilus and its crew “dominated virtually every NATO exercise they participated in,” wrote Tom Clancy in his book Submarine: A Guided Tour Inside a Nuclear Warship. It crushed speed and distance records, submerged for more than two weeks at a time, and avoided the best submarine detection systems. In 1958, it became the first vessel to cross under the North Pole. Nautilus was a prototype for the Navy’s revolutionary submarine fleet, and the reactor a prototype of the commercial reactors to come.

Nautilus remained in service for 25 years and traveled half a million miles before being decommissioned in 1980. It’s now a national historic landmark open to the public at the Submarine Force Museum in Groton, Connecticut.