Before World War II, shipbuilding in the U.S. was not a major industry. But with German U-boats sinking ships off the east coast within sight of land, it was absolutely essential to build a large, strong U.S. Merchant Marine to carry combat supplies and materials to Allied fighting forces. During World War II, eighteen shipyards in the United States built more than 3,000 “one-island” ships - the famous Liberty and Victory ships - and one third of the workforce were women. The Liberty design was a modification of an earlier British hull, with three-island ships giving way to freighters with one island, either in the middle of the ship or toward the stern. The island included the bridge and living quarters, with the engine room below. The one-island ship provided room for more and bigger hatches and so made it easier to load and unload cargo. They carried millions of troops and millions of tons of supplies to battlefields in every part of the world. Economical and simple to build, it ushered in the era of pre-fabricated mass production. 