HOW can an airplane fly slower at 200 miles per hour than another airplane flying at the same speed? That's ridiculous, of course, yet your eyes are apt to tell you it’s so, the first time you see the gigantic B-19 “hemisphere defender” in the air. This tremendous warplane is so big that when you watch it you get the illusion of slow speed, even though a smaller airplane nearby seems to have to hurry to keep up with it. Think of an airplane so large that its wing span is greater than the height of a 17-story building - that's the B-19. You could park a full-sized passenger transport under each wing, with a light bomber under each wing of each transport. You could hide a couple of light sport planes under the elevators. Mechanics can walk upright inside the wing. A railroad tank car of gasoline is needed to fill its fuel tanks. Its landing wheels, weighing more than a toneach, have to be handled witha crane. No human pilot has the strength to work the vast control surfaces. The rudder alone has 237 square feet of movable surface. The landing flaps have an area large enough for a transport wing. The pilot could no more push such surfaces around with the strength of his arms and legs than a mosquito could push a barn door open against a hurricane, so a power steering system is used. The pilot’s conventional wheel and rudder controls are attached to small control tabs on the respective main control surfaces and the action of each tab starts the big control surface moving, after which hydraulic pressure takes up the work. The ailerons are so long that each is built in two sections to prevent binding, because the wing has an up-and-down tip deflection of 12 feet under some flight conditions. Five years ago the Army Air Corps decided that it wanted to test a superairplane. It asked the Douglas Aircraft Company to swear a staff of its employes to secrecy, hang a curtain across one end of its factory, and build an aerial battleship. What was desired was no experimental airplane but a tremendous bomber, practical and complete and able to take care of itself while conducting its long-range missions. Since then four acres of drawings have been made, and 500 engineers and mechanics have spent more than 2,000,000 hours in research apd construction. The wing of the plane that they built is a tenth of af acre in size and has a spread of feet. The plane has a gross weight of 160,000 pounds, including a tptal load capacity of 28 tons. Its foux main engines develop 8,000 horsepower for takeoff, the turbine capacity of a medium-sized ocean liner. With reduced load the airplane can maintain altitude on any two engines. It could fly one-third of the way around the world nonstop. The plane carries a flight crew of 10 men, exclusive of gunners. Defensively the plane has no blind spots, every approach being guarded by machine-gun nests and small cannon, Huge and complicated as the B-19 is, its heart consists of noth-ing more than one small 12-volt storage battery. This battery furnishes the current to start the two auxiliary engines that in turn supply the current for starting the great flight engines. The two auxiliaries are mounted inside the fuselage and develop enough current to light a large department store. Hydraulic power taken from one of the main engines makes the airplane largely independent of ground facilities. The plane can operate its own hoists for changing the 16-foot diameter propellers, for lowering the main engines to the ground and raising them, and for lifting supplies on board. The retractable tricycle landing gear weighs more than a small scout-bomber. Each main tire, eight feet high, is of 24-ply construction and contains 150 miles of rayon cord and three miles of steel wire. The steel in the two main legs and the nose strut weighs two tons. Such a monster airplane requires many things not needed on smaller craft. On the B-19 the engineers installed a fire alarm system, a 24-station telephone system, and a loud speaker warning system. Steam boilers that are heated by the exhaust gases have been provided for heating the living spaces, and provision has been made for an electric stove in the galley. On an extended flight the crew may spend three days in the air. Life rafts as well as parachutes in racks are carried. Although its basic design would be suitable for a commodious 75-passenger air liner the B-19 has a strictly military interior. A gunner occupies the tip of the nose with a bombardier at his sighting instruments below and behind the gun station. The pilot and co-pilot sit side by side in the main control cabin, some 30 feet forward of the leading edge of the wing. Behind them sit the navigator and commander at their desks and behind these men are the radio operator and chief engineer. The radio system includes as much equipment as a medium-sized broadcasting station. The mechanics’ quarters are aft of the main control cabin and from their compartment the mechanics can enter the wing, walking along electrically-lighted passageways to the engine nacelles. Ordinary adjustments and minor repairs can be made during flight. The main engines drive the instrument air pumps, the big hydraulic pumps, and the de-icer pumps, as well as turning the flight propellers. Aft of the mechanics’ compartment are the auxiliary engines, refueling valves, oxygen supply, and other gear, and aft of this department is the big bomb bay. Toward the tail of the fuselage, reached by a passageway, are a wardroom and sleeping compartment, the galley and the rear gunner’s compartment in the tail. Both the main control cabin and the sleeping compartment are soundproofed and heated. An oxygen system leads to all stations on the ship and portable oxygenequipment also is provided. The wing tips of the B-19 are almost 16 feet above the ground. An ordinary boarding gangway would be impractical, so you climb a stair ladder that drops down from a hatchway in the bottom of the hull, Construction of the bomber began in a seven-story 110-ton steel jig that held the wing and center section of the fuselage in a vertical position. The nose section was built separately and the rear end of the fuselage and tail group as a third unit.