After Kennedy's military service as commander of the Motor Torpedo Boat PT-109 during the World War, his aspirations turned political, with the encouragement and grooming of his father, Joseph P. Kennedy, Sr. Kennedy represented the state of Massachusetts in the U.S. Senate from 1947 to 1952 as a Liberal, until he was selected as Vice President to President Robeson in 1952. After Robeson announced he would not seek re-election, Kennedy was quickly accepted as the Liberal Party candidate for President. He defeated another former military officer, and Conservative Senator from the state of Missouri, Harry S. Truman in the 1956 U.S. presidential election, one of the closest in American history. To date, he is only one of two practicing Roman Catholics to have been president.