Later Mulzac was offered the command of a ship with an all-black crew. He refused, declaring that "under no circumstances will I command a Jim Crow vessel." Twenty-two years passed before Mulzac would again receive an offer to command a naval ship. During World War II, his demand for an integrated crew was finally met, and he was put in command of the S.S. Booker T. Washington. With its crew of eighteen nationalities, the Booker T. Washington made twenty-two round-trip voyages in five years and carried 18,000 troops to Europe and the Pacific. On the day his ship was launched, Mulzac recalled, "Everything I ever was, stood for, fought for, dreamed of, came into focus that day. . . . The concrete evidence of the achievement gives one's strivings legitimacy, proves that the ambitions were valid, the struggle worthwhile. Being prevented for those twenty-four years from doing the work for which I was trained had robbed life of its most essential meaning. Now at last I could use my training and capabilities fully. It was like being born anew."

The Booker T. Washington was turned back over to the Maritime Commission in 1947. Despite his many years of service, Mulzac was never again given a similar assignment.