Two recently discovered videos from the late 1970s about the use of the American STU-II crypto phone.
@97448able : The TTY equipment shown in this video is a Siemens T-100, a popular model in Europe during the Cold War. It is shown here in combination with a Siemens M-190 cipher machine (a real two-way link). The M-190 uses a so-called on-time tape and is therefore unbreakable when properly used. More on the website.