After the Word War II and during the Cold War, the security in sensitive communications was ruled by Electro-Mechanical Cyphers.
Until the 1950’s the WWII the ECM Mark II was used by the NATO, when it was replaced by machines like the KL-7.
KL-7 was an electro-mechanical rotor-based off-line cipher machine, developed by the National Security Agency (NSA) and was introduced in 1952 and served for many years as the main cipher machine of the US and NATO.