This photograph was one of Carl Mydans' photo essay images for <i>LIFE</i> magazine titled "Antiaircraft Guns: How the U.S. Army Uses Them" (Dec 17, 1937).
According to the magazine caption, this mobile gun was the mainstay of America's antiaircraft defense. It could fire twenty-five 12½ lb. projectiles a minute to a height of 25,000 feet, making it one of the most destructive guns in the world at the time. Its principal purpose was to ward off attacks on military objectives such as factories, railroad stations, and munitions depots.
This photograph earned Mydans an Exhibition Award in the First International Photographic Exposition at Grand Central Palace, New York (April 1938).