Founded in 1899 by Walter D. Munson, the Munson Steamship Line began as a freight carrier between New York and Havana. It later expanded to include ports in eastern Cuba, Mexico, and the Gulf of Mexico, becoming the largest freight company on the U.S. East Coast with over 60 cargo ships. The company entered passenger service in 1919, with its first liner, Munamar, operating to eastern Cuba. Leadership passed to Walter's sons Carlos and Frank Munson, with Frank steering the company into South American routes using seized former German and Austro-Hungarian liners after World War I. The company had a British subsidiary, Crossburn Steamship Company, and briefly re-registered two of its ships in the U.S. at the start of World War I.