PEERING through the belly windows of the fuselage, the observer saw a colored signal light flashing on the ground. Over the phone he spokeito the pilot. “Circle at 800 feet, pull three flares.” Half a minute later the ground below was illuminated by the light of the three parachute flares and the observer saw long lines of trucks moving toward the front. A year ago the observer would have returned to his airdrome or sent a radio code message to report this important information, but tonight he snapped on a shielded light and rapidly sketched on paper the size and direction of the enemy movement. He added a few sentences to explain the map, fed the paper into a facsimile machine, and pressed a button. Instantaneously in the command headquarters miles away a machine began duplicating the map he had drawn. Later the red message light beside him winked on and the observer pulled a new sheet from his facsimile box, containing revised instructions from headquarters based on the activity he had reported. Observation aviation, the “eyes of the army,” can spy so efficiently on an enemy these days that most mass-troop movements and large-scale battle preparations are made at night. The result is that aerialobservers are flying by night as well as by day and have learned new tricks that help them to see in the dark. Learning what the enemy is doing is half their task; getting the information back to headquarters is the other half. The new radio facsimile machine is the latest aid for flying scouts. Voice or code radio can be drowned out by interference, it is not secret, and it can be misunderstood. Radio facsimile can’t be drowned out or garbled, can be made secret, and reproduces anything from hand-writing to maps. The military model, containing secret improvements, is about the size of a typewriter. Observation planes are the lone wolves of the Army Air Corps and affiliated National Guard squadrons. They hunt singly, rarely accompanied by protective fighters. In actual warfare they may have to fly through their own and the enemy barrages and the pilot and observer may have the uncanny experience of watching a big shell, at the apex of its trajectory, coast along beside them. Piercing the enemy lines, they use the shelter of etvery cloud they can find and watch for enemy fighters in order to avoid them. They fly high or low, rarely in the middle altitudes where they are most vulnerable to anti-aircraft fire. The planes are slower than most military aircraft and a pilot may “hedgehop” even after dark at under 500 feet to take advantage of the terrain. At high altitudes he skids and turns and changes altitude incessantly to avoid being hit, until the observer calls for straight and level flight to permit accurate mosaic photo mapping. Pilot, photographer, radio operator, gunner, and scout—and an expert in each - these are the qualifications of an observer. Every mission is different. When Major Eldo A. Peterman, commanding the 115th Observation Squadron of the California National Guard, assembles his officers, half a dozen different assignments may be passed out. If the squadron is co-operating with ground forces in summer training, an enemy force may be assumed to have occupied part of the coastline. Captain C. W. Larsen, operations officer, lays out the plans. One plane is assigned to the artillery for fire-control spotting, two others go out to get a high-altitude mosaic of the occupied area, a fourth is sent to observe enemy fleet activity, and others are as- signed on “pin-point” missions to photograph particular places. The planes are the modern O-47A observation type and carry a pilot, observer, and rear gunner and are armed with a fixed machine gun forward and a gun on a flexible mount in the rear cockpit. Electrically operated oblique and vertical cameras are mounted inside the fuselage instead of being pointed over the side. A roll of film may be 125 feet long and cost as much as thirty dollars. While the high-altitude photo planes are still out, their cameras automatically snapping eight by ten negatives that will reveal every bush from 20,000 feet, a low-flying plane roars over the clump of trees that conceals the squadron’s mobile darkroom. A can of film attached to a parachute floats down and one of the ground men recovers it. Fifteen minutes later pictures that show the enemy’s defense around its landing beach will be ready for inspection. All through the year Major Peterman keeps his officers employed on training problems. One week they may have to work out the means of locating an enemy airdrome and keeping it under surveillance until it has been destroyed. Another time they may be given the problem of locating an aircraft carrier, known to be offshore, on a moonlit night. With only a few planes the task seems hopeless but by laying down on a chart the points at which the carrier-based airplanes were seen only a few hours before and allowing for their range and speed, a narrow area inside of which the carrier has to be is determined by the officers, after which a single plane can be sent out with every expectation that it will sight the carrier. Modern wars are fought with photographs. It is possible, by photographing the same area day after day, to learn, the size and trace the movements of an army even though the men and equipment remain successfully concealed during daylight hours. Electrically timed flash pictures reveal a square mile of ground after dark. Troop commanders who think that they can move their troops under the cover of fog are foiled by infrared film that picks up ground details through the haze. An army prepares for its advance by photographing the ground in front of it. The background for every kind of activity is prepared by advance photography and even a bombing raid is preceded by observation planes that photo-map the target area. Enlargements from the negatives reveal or suggest the most likely hiding places for anti-aircraft batteries. Pilots who have the duty of destroying this defense can study their targets ahead of time. In wartime every observation flight is a separate adventure. An enemy will do everything in its power to keep its secrets from being revealed. Pursuit planes are always on the prowl for the camera plane. Rifle fire and machine-gun fire from the ground is a threat when the planes fly low. The versatile observation squadrons work with the infantry as well as with the other forces of the army. A message and streamer dropped to the ground tell the infantry the position of the enemy. The troops reply or ask questions by means of panel signals laid on the ground, long strips of cloth arranged in code. To pick up longer messages the pilot flies low over a pair of uprights, a hook dangling from the plane picking up a rope to which the message is attached.