A fully functional GPS will allow you to easily avoid running aground and it will help you navigate to your assignment or port of call. It will tell you absolutely nothing about any ship in your area. Does your car GPS tell you anything about the big Semi barreling down on you at 70 miles an hour. No it doesn’t, neither does the Navy GPS tell them about the 50,000 ton tanker barreling down them at 15 knots. That is where radar and the Mark 1 eyeball come into play in preventing collisions at sea.
There is also AIS that shows ships around you. Recreational boaters use it all the time. However, military ships don’t use AIS . I have been boating in the Puget Sound, and all of a sudden a military ship or sub comes out of nowhere because they are cloaked. If the military is not going to use AIS, they also need to take precautions to avoid collisions.