The military is a good cross-section of America (we recruit from all over the country, all races, religions and political leanings).
In my time, very few people who say grace it a prayer, so I actually don't think it's all that common. In addition to the many years of being American, I only saw grace/prayers sparsely.
And no, I do not.
My Southern is showing because many of the military folks I know would say grace….at least at family supper.
….and i know lots of people that do….half my family does, at every meal, even in restaurants.