Gunner's Gimmick

Proud, precise Sperry Corp., manufacturer of gyroscopes and fantastically complex instruments for war and peace, had special reason for pride this week: Army authorities permitted it to release details and photographs of its Automatic Computing Sight--the magic gimmick which goes a long way toward explaining the phenomenal defensive strength of U.S. bombers against enemy fighter planes.

What the gimmick does is enable the gunners to deliver aimed, murderous fire from their .50-caliber machine guns at ranges up to 1,000 yards; fighters have to press in much closer than that.

In use (but highly secret) for two years, the gun sight is a compact assembly incorporating an optical system, a small range finder and a complex instantaneous computing machine. Only arbitrary adjustment on it is a dial which the gunner sets for the wingspread (in feet) of the attacking plane. After that he frames the plane between illumined reticules (cross hairs or similar lines imposed on the field of vision), in a mirror on the sight, and keeps it framed there. He tracks it with the handle controls of his power-operated turret. When the enemy plane fills the space between the lighted lines, it is time to fire.

The gimmick does everything else, making corrections for wind pressure, the pull of gravity on the bullets and the speed of the enemy plane. Scrambling this information in its cogwheel brain, it tosses in the speed of the projectiles and automatically points the guns not to where the foe is, but to where he will be when the bullets get there. But the human element still remains: for results, the gimmick must have correct data, steady sighting.

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