"To this day the crews of UK Trident submarines can launch their weapons on their own without requiring any codes to be transmitted to activate the weapons."
Isn't this also the case with US Trident submarines? That is, codes transmitted to the vessel are used to authenticate launch instructions, not to enable the missiles to be armed. Otherwise the submarine would be unable to launch in the event that land-based communications systems were destroyed.
As far as I know, only the UK Tridents have this interesting arrangement. This link on Permissive Action Links suggests that US Trident submarines need to receive codes to unlock safes before they can launch:
"Instead of another party confirming a missile launch as in the case of land-based ICBMs, the set of keys is distributed among the key personnel on the submarine and are kept in safes (each of these crew members has access only to his keys), some of which are locked by combination locks. Nobody on board has the combination to open these safes - the unlock key comes as a part of the launch order from the higher authority."
Isn't this also the case with US Trident submarines? That is, codes transmitted to the vessel are used to authenticate launch instructions, not to enable the missiles to be armed. Otherwise the submarine would be unable to launch in the event that land-based communications systems were destroyed.