Following the fall of mainland Europe during WWII, hostile Allied actions against land-based Axis forces were generally limited to air attacks. However, as the number of those attacks increased, the number of aircraft and crews failing to return grew alarmingly: something needed to be done to provide these crews with aids to enable them to evade to safe territory or escape captivity, or losses of irreplaceable aircrew would become critical.
Britain’s MI9 and U.S. MIS-X military intelligence organisations were formed solely to support evaders and prisoners of war in occupied territories. They developed a wide variety of evasion and escape devices that were given to Allied Forces prior to operations in hostile territories or delivered clandestinely to POWs. It worked: the aids facilitated the return of thousands of men to their squadrons and units.