The Man in military uniform is a man who works in Atlanta.
After delivering Red Barclay's shipment to Atlanta, Homer and Bart needed to find a way home. Homer told Bart that "the good lord will provide." Then they noticed an engineer standing in front of a man in military uniform. The angry engineer told him that he refused to drive a train full of napalm to Springfield. He then threw his hat to the ground and the two left. Homer thanked God, picked up the hat and entered the train cabin with Bart.