The Nimitz class aircraft carriers have been in operation since 1975, replacing the Enterprise class. The first nuclear powered submarine launched in 1954. The Navy has two Mercy class floating hospital ships to help with disaster relief and humanitarian efforts.
As of 2015, 10 Nimitz class aircraft carriers are active, and each of them is powered by two nuclear reactors and home to more than 5,000 crew members. Seven of the carriers are named after U.S. presidents including Abraham Lincoln and George Washington. These carriers are designed for a service life of more than 50 years, needing only a single refueling during that time, effectively giving them unlimited range.
The USS Nautilus, the first nuclear powered submarine, is the sixth ship named Nautilus and has been a museum since 1986. In 1958, the Nautilus was the first ship in the world to cross the North Pole. The hospital ships USNS Mercy and USNS Comfort launched in 1986 and 1987, respectively. Mercy mainly patrols the Pacific and Indian oceans while Comfort is on duty on the opposite side of the world in Latin America and the Caribbean. Each ship has 12 operating rooms and can function as a 1,000 bed mobile hospital.