If the Navy does use Google+, it will be running alongside its Facebook, Twitter and YouTube accounts. The Navy has been using these social networks to send out news, videos and pictures of its daily affairs, so that the families of the crew can keep in touch while they’re out at sea.
At the moment they’re holding Google+ under consideration because they’re not sure of its limits, strengths and weaknesses yet (as if Facebook is any more secure) and also because the service isn’t as widely used. But if they already support all those other networks, there’s probably no harm in adding one more. Apps that function with multiple networks should be sprouting up in droves soon enough, and having to update a few accounts at once shouldn’t be much of a problem.