Could anyone explain what the inscription on a headstone in Arlington Cemetery mean?

I am trying to establish if a John Quinn buried in Arlington Cemetery is my Uncle. I know of a headstone there which bears the inscription- John Quinn Ireland GM2 US NR ww2 July 1885 - April 1966. Could someone enlighten me as to what the letters GM2 and the R on us nr actually mean I did have an Uncle who served in the US Navy. If I could find out exactly where in Ireland this John Quinn came from then it would establish if it is my Uncle or not as there are undoubetdly many John Quinn's How would I get more clarity on the details as it would be nice to know I have this right I live in Ireland Many thanks