Of all the airplanes ever built that have contributed in some measure to aviation progress, there is one which has far surpassed all others in faithful service, dependability, and achievement. It has been parked on the ramps of the world’s air terminals for over thirty years. It was born during the days of wooden propellers and is still flying as we pass from the jet age into the era of space flight. This book is about that airplane: its birth, its development, its adoption by the airlines and the military services, its uses in World War II and Korea, its conversion to civilian use after the wars, its innumerable feats as an angel of mercy, its employment as a jack-of-all-trades, and, finally, its future. - Introduction.