To the best of my recollection, ALL U.S. Navy ships must have qualified navigators and they must be well versed in the use of sextants, among other navigational aides. The U.S. Merchant Marine vessels are likewise required the Capt. and the first officer to be certified navigators.
The degredation of non-military
GPS signals is not as uncommon as you might think, especially since 9/11. Every time a rocket launch (friendly or otherwise) is detected, a decision about the
GPS signals is made. Also, there are places on the Globe that do not get good satelite coverage, at least not 24/7.
Sole reliance on electronic aides is just too huge a risk to take with Murphy considering the potential consequences. Besides, using a sextant is not that hard. All it takes (like sailing) is practice. ;^)
~ Happy sails to you ~