The Type B ship is a United States Maritime Administration (MARAD) designation for World War II barges. Barges are very low cost to build, operate and move. Barges were needed to move large bulky cargo. A tug boat, some classed as Type V ships, could move a barge, then depart and move on to the next task. That meant the barge did not have to be rushed to be unloaded or loaded. Toward the end of World War 2, some ships that had not been completed in time for the war were converted to barges. US Navy barges are given the prefix: YWN or YW. Due to shortage of steel during World War II, concrete ship constructors were given contracts to build concrete barges, with ferrocement and given the prefix YO, YOG, YOGN. Built in 1944 and 1945, some were named after elements.