AMERICA paid a toll of hundreds of lives and millions of dollars in destroyed property to saboteurs during the first world war and today Uncle Sam is resolved that history will not repeat itself. Our most vital defense industries are already safeguarded against foreign spies and agents, and similar precautions are being taken by other industries also important in defense. Munitions plants and aircraft factories, especially, are on guard inside and out. Armed sentries are on patrol 24 hours a day and others keep watch from observation towers. Many ingenious ways of guarding against subversive agents have been perfected, but a large number of these are kept secret to prevent spies and would-be saboteurs from knowing what to expect. One protection being widely adopted is the use of infrared fences that consist of invisible strands of infrared light. Such a fence automatically turns in an alarm when one of its strands of “black light,” which is invisible to the human eye, is broken by an intruder. Presence of the fence is impossible to detect when both the source and receiver are properly hidden. One recent improvement to the infrared fence is the use of beam splitters, each of which absorbs a small percentage of the ray, along the line of the beam when the beam is being thrown for a long distance out of doors, as along the side of an airport. If an intruder walks across the beam, only the beam splitters between the intruder and the electric-eye receiver are affected, showing at once the exact area where the trespass occurred. One clever use of the beam is to install an infrared system inside a vault where blueprints or other valuable papers are kept, in cases where the vault must remain open for hours at a time for the convenience of employes. The invisible beam system is set up so that it automatically turns on a motion picture camera that runs for a short time after the beam has been broken. Employes who have authority to enter the vault make a hand signal after they enter which is recorded by the camera. One of the hardest places in the world to enter, if you don’t have bona fide business there, is the main plant of the Douglas. Aircraft Company in Santa Monica, Calif., where more than $300,000,000 worth of military airplanes are being built. Eighteen thousand employes walk in and out every day but a stranger can’t. Each employe displays his badge and an identification card that contains his fingerprints and photograph to the guards at the gate, yet if a spy counterfeited a badge and card or stole them from an employe and tried to get in he would still be caught. Nerve center of the Douglas protection system is the combination police and fire headquarters that is connected to all parts of the plant and grounds by telephone systems, automatic alarms, and fire-alarm networks. Any guard can call in on a direct wire if he sees something out of the ordinary and the whole communication layout automatically switches over to a tamperproof emergency power source if the ordinary current fails. The police force consists of 162 officers, all of whom have had previous military or civil police experience. The force is twice as large as the average police department for a city of 100,000 people and even includes motorcycle police for escorting trucks that are hauling important or secret material from one plant to another. To join the force, an applicant has to pass tests much harder than the usual police requirements and he must be an unusually good marksman. In addition, the plant is under the scrutiny of Army and Navy representa tives as well as Federal Bureau of Identification operatives whose identities are unknown even to the police staff. If you apply for a job in the plant, you are first photographed and fingerprinted and then you wait ten days while your statements and background are checked. Once on the payroll, you wear a badge that restricts you from every part of the plant except the area in which you work. At irregular intervals the contents of all lunch boxes and other packages carried by employes are inspected. No outsider can enter the plant unless he has an appointment with an official inside and he can’t get through the entrance until his appointment is confirmed. Only American citizens can enter under any circumstances and no visitor can wander around at will. If his appointment is in the engineering department he must undergo a second scrutiny and sign a pass book upon entering and leaving. No one except special employes who have sworn to observe particular secrecy is permitted in the restricted parts of the plant where confidential work is being done. Even those who are working on a secret project can’t gain admittance to the restricted area until they have shown their special credentials to a guard. Then the guard opens a barred entrance door by remote control. Fire is one of the most dangerous weapons of the saboteur and at Douglas extraordinary precautions are taken against it. Each working shift has a fire chief who has given special training to hundreds of the men in his shift. Fire equipment that includes carbon dioxide tanks and asbestos suits is scattered through the plant and the company maintains a large modern fire rig that is also suitable as a crash wagon for handling accidents at the airport. Every one of the smart tricks employed by professional arsonists has been studied and prepared for. The fact is that fires, most often caused by carelessness, are more prevalent during times of re-armament simply because of the rush of work, and this is one of the reasons for taking elaborate precautions against fires. The Santa Monica plant and the other Douglas divisions are being augmented by a new $12,000,000 aircraft factory at Long Beach in which, in addition to the present kinds of protection, camouflage that will hide it from air observers is being provided. Even if an enemy bombing crew knew the factory’s location it would have trouble picking out the buildings and if the plant should be bombed the damage would be held to a minimum because of the scattered arrangement of the buildings. Already close to completion, the decentralized factory will consist of 12 buildings so placed over 200 acres that each building is separate from the others. The plant will be virtually invisible at night, both from the ground and the sky, owing to its landscaping and the fact that light traps and filters will prevent light leaks. Even the entrance to a railroad freight terminal in one of the buildings will be protected by giant double lightproof doors. The factory will be self-contained as far as power and gas are concerned, independent of outside sources. The lessons in protection that are being learned at Douglas and at the other aircraft factories are being applied rapidly in automobile plants, steel mills, and even in petroleum refineries. In every industry connected with the re-armament program the workers are being cautioned to report every action or circumstance that seems in any way suspicious. Even though only one in a hundred such tips may lead to uncovering an actual case of attempted sabotage, constant vigilance of employes may save their lives and jobs. This is one of the most important factors in making America’s defense both spy and sabotage-proof.