Applegate developed the techniques outlined in the book during his work with William E. Fairbairn, who had previously developed his own techniques while working for the Shanghai Municipal Police from 1907 to 1940. Fairbairn drew heavily on Chinese martial arts, which he simplified and tailored to the needs of police training in one of the world's most crime-ridden cities, due to its history of crime related to the opium trade, the rebellion, and the activities of Triad gangsters. His result was the development of Defendu, widely considered the first of what became known as modern combatives. Applegate's techniques are heavily based on Fairbairn's Defendu, enhanced with feedback from the OSS operatives who put his techniques into action during World War II.