Test flights of the Trident missiles used GPS payloads to calibrate and test the inertial guidance system.
The Trident missile system has multiple-independently-targeted warheads: I don't know how they work. Nothing I've seen suggests that they use GPS (there are problems with reception, lock-in, and speed), but I don't have any specific information.
One of the first possible suggested uses for a proposed satellite navigation system was to provide location information for launch sites, to be used with alternate-launch-site missiles. I don't think GPS is used by submarines to get accurate launch location information (in any normal scenario, they would be underwater for long periods before launch), but again, I don't have any specific information.