The document describes the development of aerial retrieval systems for extracting personnel from difficult terrain. It discusses the All American system used in World War II and the Korean War to retrieve agents and downed pilots. It then focuses on inventor Robert Fulton Jr.'s development of the Skyhook system in the 1950s, an improved system commissioned by the Office of Naval Research. Fulton refined his system over many test flights, increasing payload weight until the retrieval line broke and developing an effective locking device to secure the line to aircraft. By 1958, the Skyhook system was fully developed into an effective means of aerial extraction.