7774th Signal Battalion
(Source: Jack Emanuelson, 1954)
I want to include this one because there is a little story. Note that the key on the first row left is blank. I do not know what its original function was, but it was not connected. However, we had fun with new cryptographers. The machine sat on a desk. Directly behind the machine, a wooden box was attached to outside of the desk and a small thermite device placed in the box. All of the thermites were wired to a master control box. The idea was that in case the cryptocenter had to be evacuated and everything destroyed, the thermites would be placed on top of the machines with rotors inside and set off. So, we would tell the new operators to be careful not to hit the blank key, since that key would set of the thermite bomb. The joke didn't last for long, but we caught a few believers.