From the Wall Street Journal:
Heinlein brought to his work a unique combination of technical savvy–based largely on the engineering training he’d received at the U.S. Naval Academy and a career in the Navy cut short by tuberculosis in 1934–and a broad knowledge of history and foreign languages. Bemoaning the state of U.S. education in the 1970s, he wrote that “the three-legged stool of understanding is held up by history, languages and mathematics . . . if you lack any one of them you are just another ignorant peasant with dung on your boots.” Heinlein was certainly no ignorant peasant.
Though he later became well known for his anticommunism, Heinlein in the late 1930s indulged in both leftist and isolationist politics. He sold his first science-fiction story in 1939 for $70, “and there was never a chance that I would ever again look for honest work.”