That's appears to be evidence given to a select committee - so it's one person's view.
AFAIK subs don't use GPS underwater - and missile subs spend most of their missions underwater. The missiles themselves use inertial (hence the dependency of knowing the launch point) and star-sighting:
"GPS has been used on some test flights but is assumed not to be available for a real mission."
I'd be very surprised if the sub don't go to see with at least some target data - kinds of defeats the purpose of the entire system which is set up to give UK Trident sub commanders a surprising amount of leeway:
AFAIK subs don't use GPS underwater - and missile subs spend most of their missions underwater. The missiles themselves use inertial (hence the dependency of knowing the launch point) and star-sighting:
"GPS has been used on some test flights but is assumed not to be available for a real mission."
https://en.wikipedia.org/wiki/Trident_%28missile%29
I'd be very surprised if the sub don't go to see with at least some target data - kinds of defeats the purpose of the entire system which is set up to give UK Trident sub commanders a surprising amount of leeway:
https://en.wikipedia.org/wiki/Letters_of_last_resort
[Edit: For the record - I am rather passionately anti-Trident and would strongly prefer the UK didn't have them].