Before Jackie Robinson became the first black man to play baseball in Major League Baseball, he was a second lieutenant in the United States Army, having joined in 1942. He was discharged in 1944 and began playing professional baseball.
During his time in the Army, Robinson was court martialed for not following a bus driver's directive to give up his seat on a bus. According to Biography.com, his good reputation and the support of those who came to his aid helped in his defense, and he was discharged honorably from the service. Robinson first played in the Negro leagues, but was contacted by Branch Rickey of the Brooklyn Dodgers who wanted him to play for them. In 1947, Jackie Robinson became the first black player to take the field in a Major League Baseball game.