After four years of building, the gigantic “B-19" - largest military aircraft the world has ever seen - has tried out its own element, the air. Its four 2,200-horsepower engines roaring music to the ears of the engineers and mechanics who built it, the monster silver ship lifted from the runway at Clover Field, Santa Monica, Calif., and flew low past the throngs gathered outside the Douglas plant where it was developed. The fledgling warbird performed creditably on the first trial of its wings. It was off the ground in nine seconds, after rolling across 1,500 feet of runway; flew out to sea, circled to salute the Douglas workers and then headed for March Field, the army base, 75 miles away. A smooth landing was made after 56 minutes in the air. Maj. Stanley H. Umstead, army test pilot, was at the controls for the historic flight. Six other army and Douglas men were aboard; the normal operating crew will consist of ten men. Less than one-fifth of its 11,000-gallon fuel capacity was carried. The plane, with 212-foot wing spread and 132-foot fuselage, is rated at 41 tons empty and 82 tons fully loaded, including several tons of bombs.