The first C-5A 'Galaxy' started flight testing on June 30, 1968. Flight tests revealed that the aircraft exhibited a higher drag divergence Mach number than predicted by wind tunnel data. The maximum lift coefficient measured in flight with the flaps deflected 40-degree was higher than predicted (2.60 vs. 2.38), but was lower than predicted with the flaps deflected 25 degrees (2.31 vs. 2.38) and with the flaps retracted (1.45 vs. 1.52). [Wiki]