Good gunnery of German ground defenses against airplanes has been attributed to the use of a new type sonic or accoustical locator installed in a network of stations throughout western Germany, the Low Countries and occupied France. The instruments reveal the altitude, direction and speed of planes even when they are hidden by clouds, and this information is used in directing antiaircraft guns. However, instead of attempting to hit individual planes, the gunners lay a “curtain” of exploding shells two to four thousand feet in height and across the path of the aircraft at their approximate altitude. If a plane flies through the cuirtain barrage it has little chance of escaping damage. Groups of locators and gun crews dot the countryside at intervals of 20 to 30 miles, it is said, and information concerning the courses, speeds and altitudes of raiders is telephoned to central points where it is digested and forwarded to anti-aircraft batteries. German technicians say that when operating against a plane flying at 28,000 feet the sonic locators are subject to errors of less than 40 inches.