http://bkg5ofjslnbyqvu55sjonpdyp3wmfsgq23u7vpk3wxn7ewgdeocpgwid.onion?page=article&article=The+Historic+Use+of+Dead+Drops+in+Espionage+and+Spycraft.html
Over time, these methods evolved to suit the needs of modern espionage agencies. By the 20th century, during the Cold War, dead drops became a hallmark of espionage between rival powers, especially the United States and the Soviet Union.