Tests of safety glass three inches thick, designed for protection of pilots and gunners in warplanes, prove it, will stop even the heavy bullets of .50-caliber machine guns fired at right angles from 100 yards away. Two-inch glass of the same type. will stop bullets of the ordinary rifle-caliber machine guns. The heaviest bullet shatters and powders the glass at the point of impact but fails to penetrate it. Since windshields and turrets on airplanes are always streamlined and present a sloping ¢ front to the enemy bullet, thinner glass than that tested nearly always would offer sufficient protection.