Harry Osborn, First Lieutenant U. S. Army Air Corps, banked his wide-winged bombing plane in an easy, swooping curve. In the distance New York's white pinnacles caught the sun above a blue-gray billowing of twilight ground-haze. A faint smile lifted the corners of his lips as he glanced overside, saw a train crawl along shining rails and come to a halt. Brown dots appeared from the passenger car behind its locomotive and clustered in ordered confusion about the other oblong that completed the train's complement.What appeared from his altitude to be a rather large pocket-handkerchief slid from the car and spread out on the grass. A metal tube glittered in the sun, came into motion, swivelling to the east. It looked like a cap-pistol, but Osborn knew it to be an eighteen-inch railroad gun.He slanted down through lambent air. The terrain below was flat, lushly green. It was entirely vacant save at the very center of its five-mile sweep of marsh. Here a small hut was visible in the middle of a hundred-yard area ringed by a water-filled moat.Two manikins stood before the structure. One was clothed in o.d., the other in black. The civilian's tiny arms gesticulated, and he went into the house. The army man moved sharply into an automobile and sped in the direction of the waiting artillery train."Five minutes to zero, Harry." The voice of Jim Raynes, his observer, sounded in the pilot's earphones, "What's the dope?"