Beginning to roll off assembly lines in large numbers, the army’s newest 28-ton medium tank is acclaimed the most powerful armed fighter of its size and type. It carries a 75-millimeter field gun, a 37-mm. anti-tank and anti-aircraft gun mounted in a power driven turret, as well as several machine guns. In tests the speedy “fortress” lumbered through sandy fields at 25 miles an hour, firing its cannons with remarkable accuracy.