ONE MAN COULD turn both keys in the activation sequence - which was NOT supposed to be do-able.
During periodic testing of the control room -to- silo control links, a single man was left to activate the keys to test the wiring systems. The 2 consoles were 8 - 10 (or so) feet apart, and designed to REQUIRE 2 men to activate the firing sequence at the same time.
Using 2 nails and a length of sting, the ingenious control house tech put one nail above the second key control, the second nail through the head of the key, tied the string to the second nail (key-head nail) and ran the string across the top nail and over to the second key station.
BINGO! He could turn BOTH keys simultaneously - one by hand, the other by pulling on the string.
When observed (caught) doing this testing, he was told to never discuss it, and the repercussions went like a silent tidal wave all the way to the top.
I still don't know how this was resolved - but I imagine the key consoles were outfitted with additional locks that required pushing an actuator button or something, requiring 2 hands to activate.