IIRC my Father in Law (also a retired Marine, he was a pilot, what a guy he was!) tried to decline his SS but there was something that forced him not to. I can’t remember what it was, but it may have been that he would lose medical coverage, which reverted to Medicare once he hit that age, rather than whatever the military was doing (CHAMPUS?)
You are sort of damned if you do...
BTW there is nothing wrong with some people receiving a govt check, and the military comes to mind. Thanks for your service and God bless you.
susie