Back in the late 1960’s I was trained as a Crypto Repair Technician in the US Air Force. The 10 month long training was at Lackland AFB in San Antonio, TX. This was one of the longest technical training classes the Air Force had.
I was trained on the; KY-3, KW-7, KW-26, KG-13, and the British BID-610. Only the KY-3 was voice and was used mostly by Congress, the State Department, and the Pentagon. It was the size of a small washing machine. The KW-7 was more or less portable (only because it had handles on the side) and was used by airborne and remote teletype operations. The others were rack mounted and were also used with teletype systems. The KW-26 still used vacuum tubes, the others were discrete components, no integrated circuits at that time. These crypto systems survived the Korean War and every War since then.
The KW-7 and the KW-26 are still in use today. One may ask why the KW-26 that uses vacuum tubes from the 1950’s is still being used today? Because it will survive an Electromagnetic Pulse (EMP) attack.