World War II United States Merchant Navy was the largest civilian Navy in the world, which operated during World War II. With the United States fighting a world war in all the world oceans, the demand for cargo and fuel was very high. Cargo and fuel was needed around the world for the United States Navy, United States Army, United States Marine Corps, United States Army Air Forces, United States Coast Guard and the support of the allied nations of the United States. American steamship companies chartered ships from the Maritime Commission and War Shipping Administration to meet the demand. Many United States Merchant Marine ships were newly built in the Emergency Shipbuilding Program, other ships were older World War I ships that were put back in service, or private ships acquired under Em