I wonder if each submarine actually has two of these, physically separated, that have to be simultaneously activated.
No they do not. There are two triggers in a US Submarine missile control center (MCC).. one is white and for training and the other is behind a safe at the top of the MCC console (as I remember it.)
The Captain of the Submarine has a button in the Conn (the main control room of the Submarine where the helm resides) (in his chair as i remember it) called “Captain’s permission to fire.” That button must be engaged before the trigger in MCC can launch a missile.
Once the “Captains Permission to Fire button” is engaged the Captain issues the order to “Shoot” (the term “fire” is not issued as it could cause the confusion that a fire has broken out on the ship) and the Weapons Officer pulls the trigger. At that point the end of the world as we know it concludes.
I believe the two “triggers” are for ICBM launches from Air Force silos....