Construction of the airfield began in July 1942, and its immense hangar soon took shape after the original plans were modified to increase the building’s height and length, likely to accommodate larger B-29s, although crews at Lewistown trained exclusively on various models of B-17s. On site, construction crews laid out the lumber for the bowstring trusses, assembled them for fit, then took them apart to cut grooves and glue and spike the pieces together. The airfield accommodated one squadron in training at a time, with nine B-17s to a squadron, and five of the hangar’s six bays could hold five of the huge planes, packed closely together. Before a training mission, B-17 crews lined up outside the hangar to await the bombardier, who was escorted by armed guards to the Norden bombsight shelter to retrieve the top-secret device and then escorted to the hangar and the plane, and the process was repeated when the crews returned.