NEXT CAME THE Y1B-17: Thirteen were delivered in 1937. One stalled, spun down over Langley Field, recovered, landed safely. Recording instruments showed it had held up under greater stress than it was designed to stand.

THE B-l7A WENT HIGHER: Equipped with turbos, it topped all previous service ceilings, gave maximum performance above 30,000 ft. To range, speed, bomb load, firepower, the B-l7 added another advantage: altitude operation.