As time went on, competing Axial turbines became dramatically more efficient and powerful, a second set of reduction gears was introduced in most cutting edge U.S. naval ships of the 1930s. The improvement in steam technology gave the U.S. Aircraft Carriers a clear advantage in speed over both Allied and Enemy aircraft carriers, and so the proven Axial steam turbines became the preferred form of propulsion until the 1973 oil Embargo took place. The oil crisis drove the majority of new civilian vessels to turn to Diesel engines.