Takepart notes:
Of course, Robinson didn’t begin his fight for equal rights overnight. While enlisted, Robinson was court-martialed for refusing to sit at the back of the bus — eleven years before Rosa Parks. Faced with multiple offenses, including public drunkenness (even though Robinson did not drink), the UCLA standout was acquitted of all charges by an all-white jury.
American Heritage Magazine has this introduction to the charges (and a fairly decent history of the case):
ON JULY 6, 1944, Jackie Robinson, a twenty-five-year-old lieutenant, boarded an Army bus at Fort Hood, Texas. Sixteen months later he would be tapped as the man to break baseball’s color barrier, but in 1944 he was one of thousands of blacks thrust into the Jim Crow South during World War II. He was with the light-skinned wife of a fellow black officer, and the two walked half the length of the bus, then sat down, talking amiably. The driver, gazing into his rear-view mirror, saw a black officer seated in the middle of the bus next to a woman who appeared to be white. Hey, you, sittin’ beside that woman,” he yelled. “Get to the back of the bus.”
A more “official” version is at the National Archives; “Jim Crow, Meet Lieutenant Robinson: A 1944 Court-Martial.”