John:

I believe you are mistaken about the SS Ludington (X-120) being a Naval supply ship. That was an Army ship and had a U.S. Naval Armed Guard gun crew on board as I understand it.

I have Colt 1090016, which was 1 of 4 pistols on that ship (yours being listed as well). Charlie Pate wrote and interesting article a year or two back on the U.S. Army ships and featured my pistol, among others.