In 1948, the world’s first mobile (i.e. moveable) betatron began operation at the U.S. Naval Ordnance Laboratory, White Oak, Md, in a building with 3-foot-thick reinforced concrete walls to protect persons. Using 10 million volts to accelerate electrons, the betatron produced a sharp beam of high-energy X-rays capable of penetrating 16-in. (40 cm) of steel. The limit for earlier industrial machines was 12-in. (30 cm) of steel. Moved by a crane, the new betatron was also unique because it could be aimed in any direction. The instrument was used in studies of the complicated internal assemblies of mines, torpedoes, and other ordnance equipment. It was built by General Electric Company, Schenectady, N.Y.«