During World War II the ability of American ground forces to advance in the face of fierce resistance was largely dependent on the precision of artillery barrages. Aerial observation was frequently the only effective means to locate enemy targets. For this mission the Army air corps used prewar light civilian airplanes (usually reconfigured Piper Cubs) known as Grasshoppers for their ability to take off from and land in tight places like dirt roads, grass fields, and ships. In addition to pinpointing enemy artillery, these aircraft were often assigned other missions--medical evacuations,...