A FLIGHT of planes representing enemy aircraft had been ordered to attack an unknown target in southern California and the defending forces had mobilized to track down the planes. At the nerve center of the defense network in Alhambra groups of army officers and civil technicians were watching the operation of their latest idea, the new aircraft warning service. From the long telephone table a bell jingled six times and an operator lifted his receiver. “Message center, go ahead,” he said. “Flash flash 5 Ventura 215 seen Ventura 9 large bomber multiple motor monoplane southeast high 10:58 that's all.” Nine enemy bombers headed southeast had been spotted high above Ventura by a civilian observer. Checking the words on a chart in front of him, the message clerk passed the sheet to an army officer who had the job of plotting the course of the flight. On a large map at one end of the big room a red light that marked the location of the report flashed on and details of the message appeared on a moving tape on a translucentscreen overhead. By now other dispatches were coming in over the battery of phones. Teletype machines were chattering and operators at the radio posts were taking down other messages. On the big map another red light showed the latest location of the planes and the path along which they had passed was marked by bulbs that glowed more dimly. Looking at the map and the charts in front of him, the plotting officer made his decision. “Probable objectives are Douglas airplane factory and the oil refineries at the harbor. Warn Santa Monica to expect hostile aircraft at 11:15,” he ordered. The defending squadrons at adjacent airports had already been warned by radio and now special air-raid signals were transmitted to civil authorities over the civil advisory circuits. In each town involved authorities were “alerted” for possible fire suppression, rescue of trapped civilians and evacuation. At a table beside the map a sergeant was watching a cathode-ray tube. Suddenly the glowing line on the face of the tube began to waver. “Formation passing over robot listening post number one,” the sergeant reported and at the same time the room was filled with the sharp roar of airplane motors from a loud speaker below the tube. The huge mechanical ears that the army uses to detect distant airplanes require from eight to ten men to operate and in the recent California tests an untended robot ear was tried out for the first time. Guarding a lonely mountain pass more than 100 miles away, the ear picked up the sound of the invading planes as they passed overhead and transmitted it along a 66,000-volt power line as carrier current to the message center. The cathode tube gave a visual sound track of the flying planes, permitting detection and identification of the type at long distance. Ultimately the robot listening post may be improved to report the altitude, direction of flight and even the number of planes that it “hears.” For three days last summer the Pacific coast frontier was in a state of military preparedness. General Air Corps maneuvers gave the aircraft warning service a chance to prove its efficiency. Message centers at Seattle, Portland, San Francisco and Alhambra easily kept track of the flights from the reports flashed in by hundreds of special civilian observers who used a vast network of communication lines. On an average two minutes elapsed from the time an observer first saw the planes until he contacted the message center. The warning service was developed in conferences between army authorities and officials of the Southern California Edison company after it was realized that in an emergency valuable time might be lost in creating a network to report the presence of enemy airplanes. The present organization consists of trained men in the employ of public utilities and other agencies, and is ready for instant operation at any time without diverting men from their usual duties or commandeering public channels of communication. In the southern California test area a territory as large as New England is protected by men at 245 reporting stations. For the last three summers, the first two times in secrét, drills were held to test the observers in speed and accuracy. Nucleus of the warning system is the Edison company’s 6,500 miles of private telephone lines and 17,000 miles of light and power lines that crisscross the area and extend far into the mountains. Interconnected with these are the communication circuits of other utilities. Telegraph company linemen, station agents of the major railways, mountain lookouts of the forest service, lighthouse keepers along the coast, and navy observation stations on offshore islands all link together to form a voice, teletype, and radio network around Los Angeles that would be extremely difficult to penetrate without detection. As organized, the warning service is merely an organization to warn the army and the population of incipient attack. At the message center are the facilities for throwing switches for a blackout as protection against night air raids although authorities are undecided about the value of a blackout in a highly electrified community. A general power cut-off would result in serious stoppage in steel hills, petroleum refineries and airplane factories. The idea of the aircraft warning service is an outgrowth of an older plan intended to organize emergency assistance in time of stress. Unknown to most of the inhabitants, a major disaster plan has been prepared for Los Angeles city and county and for a number of other cities and counties in the west. In case of any such major catastrophe as a devastating earthquake, an uncontrollable pestilence, or a destructive air raid, a behind-the-scenes rescue and rehabilitation organization will immediately begin to function. The plan coordinates into a large efficient organization much of the public and private resources of the area. The American Red Cross, fraternal organizations, law-enforcement bodies and fire departments, ex-service men and other groups, all have been furnished with stand-by orders as to what each member should do. The efficiency of such a plan depends on its details and the emergency council of Los Angeles county has tried to foresee every possible contingency. Golf courses, parks, race tracks and other open areas adjacent to dense population centers are listed as possible refugee camps, the availability of uncontaminated water and the furnishing of medical supplies to the refugee centers has been studied, and the location of food supplies has been noted. Chests of maps have been prepared, available only in time of a major disaster, that show all public utility lines and pipes in the area and the location of all key valves and switches that might be needed for shutting down or furnishing electricity, water, and gas. Members of the emergency organization have written instructions as to the location of supplies of motor fuel, lubricating oil and construction equipment. Arrangements have been made for drafting airplanes and boats. The larger fleets of taxicabs, automobiles and trucks are listed. Portable emergency illumination and public-address systems would be furnished by motion-picture studios. Armored cars would be available from bank-messenger concerns. Alternative methods of communication have been prepared in case the ordinary systems should fail.