Prior to 2008, twelve U.S. Presidents reportedly did not serve in any branch of the military or the reserves before becoming Commander in Chief.  They are: John Adams, Thomas Jefferson, John Quincy Adams, Martin Van Buren, Grover Cleveland, William Taft, Woodrow Wilson, Warren Harding, Calvin Coolidge, Herbert Hoover, Franklin Roosevelt and William Clinton. (While Thomas Jefferson is often listed as having had no military experience, some sources cite his having commanded a Virginia regiment.)

Upon his inauguration, President Barack Obama will become the 13^th Commander in Chief of U.S. armed forces with no previous military experience.

—Source: Wikipedia