There's a code lock - the PAL - on US Tridents, not just the launch keys. Anecdotally and non-authoritatively I've heard that there are offline backup codes in

There's a code lock - the PAL - on US Tridents, not just the launch keys. Anecdotally and non-authoritatively I've heard that there are offline backup codes in a safe accessible to the command crew (which is the mechanism I refer to above). "Last strike" is arguably a necessary component of a submarine deterrent since it means even a surprise decapitation strike carries the risk of a retaliation. It's certainly why the UK delegates launch authority to the captain (again, after a procedural verification of the destruction of the chain of command). God, this stuff is frightening.