Complex sentence: After her World War I service ended, "Siboney" reverted to the Ward Line, her previous owners, for whom she was employed in transatlantic service until 1921, and on New York to Cuba and Mexico routes through 1940.
Split into simpler sentences: After her World War I service ended, "Siboney" reverted to the Ward Line, her previous owners. The ship was employed in transatlantic service until 1921, and on New York to Cuba and Mexico routes through 1940.