The four Richmond Shipyards, located in the city of Richmond, California, were run by Permanente Metals and Kaiser Shipyards. The Richmond yards were responsible for constructing more Liberty ships during World War II (747) than any other shipyard in the United States. Liberty ships were chosen for mass production because their somewhat obsolete design was relatively simple and their triple expansion piston steam engine components were simple enough that they could be made by several companies that were not highly needed to manufacture other parts. Ship building was given a high priority for steel and other needed components, as the German U-boats until 1944 sunk more ships than could be built by all the shipyards in the United States. The United States shipyards built about 5,926 ships in World War II plus over 100,000 more smallcraft made for the U.S. Army naval components.