Latest weapon for fighting air raiders is a powerful new antiaircraft gun capable of hurling shells to heights beyond 30,000 feet. Its caliber is 4.7 inches, or 120 millimeters, and it is said to be one of the mightiest weapons ever turned against high-altitude bombers. The possibilities of such a gun were first determined mathematically in the United States Ordnance Department office, and then were tested by retubing a larger gun to 4.7-inch caliber.