The US Naval Academy was founded in 1845 to train the future officers of the US Navy and US Marine Corps. Academy graduates serve at least five years as Navy or Marine Corps officers. The school has about 4,000 students, known as midshipmen (freshmen as plebes). The Navy pays for the tuition, room and board, and medical and dental care of Naval Academy midshipmen, who are on active duty in the Navy. By order of Congress, women were first admitted in 1976; they make up 20% of the class of 2009. Notable graduates include President Jimmy Carter, Perot Systems founder Ross Perot Sr., retired NBA star David Robinson, Arizona Senator and presidential nominee John McCain, and NASA astronaut and Rear Admiral Alan Shepard.