Conversion. Automobiles to 40 mm. anti-aircraft guns. 40 mm. anti-aircraft gun barrels for the U.S. Army are machined and finished in a former automobile plant. First they are cut to size and then their centers located. After that, they go down long machining lines where they are finished by mass production methods. Never before has any manufacturer attempted to make gun barrels of this size on a mass production basis. Chrysler Corporation, Highland Park, Detroit