Background: Robert Anson Heinlein (; July 7, 1907 - May 8, 1988) was an American science fiction writer. Often called the "dean of science fiction writers", his sometimes controversial works continue to have an influential effect on the genre, and on modern culture more generally. Heinlein became one of the first American science fiction writers to break into mainstream magazines such as The Saturday Evening Post in the late 1940s. He was one of the best-selling science fiction novelists for many decades, and he, Isaac Asimov, and Arthur C. Clarke are often considered the "Big Three" of English-language science fiction authors.
Context: Heinlein's experience in the U.S. Navy exerted a strong influence on his character and writing. He graduated from the U.S. Naval Academy in Annapolis, Maryland with the class of 1929 and went on to serve as an officer in the Navy. He was assigned to the new aircraft carrier USS Lexington in 1931, where he worked in radio communications, then in its earlier phases, with the carrier's aircraft. The captain of this carrier was Ernest J. King, who later served as the Chief of Naval Operations and Commander-in-Chief, U.S. Fleet during World War II. Heinlein was frequently interviewed during his later years by military historians who asked him about Captain King and his service as the commander of the U.S. Navy's first modern aircraft carrier.  Heinlein also served aboard the destroyer USS Roper in 1933 and 1934, reaching the rank of lieutenant. His brother, Lawrence Heinlein, served in the U.S. Army, the U.S. Air Force, and the Missouri National Guard, and he rose to the rank of major general in the National Guard.  In 1929, Heinlein married Elinor Curry of Kansas City in Los Angeles, and their marriage lasted about a year. His second marriage in 1932 to Leslyn MacDonald (1904-1981) lasted for 15 years. MacDonald was, according to the testimony of Heinlein's Navy buddy, Rear Admiral Cal Laning, "astonishingly intelligent, widely read, and extremely liberal, though a registered Republican," while Isaac Asimov later recalled that Heinlein was, at the time, "a flaming liberal". (See section: Politics of Robert Heinlein.)
Question: When did he go to the navy. Whats the answer?
He was assigned to the new aircraft carrier USS Lexington in 1931,