"GI" was short for (take your pick) "galvanized iron" or "government issue". Thus the big garbage cans that I had the excruciating pleasure of scrubbing out by hand when on KP duty were "GI cans". There are those who used to think "GI Joe" came from that.

But everything that a soldier had, ate, fired, or wore was government issue, of course, and standardized to a fare-thee-well. Just as the Army wanted to think of the individual soldier: A standardized manpower unit, so to speak. Thus, the generic soldier "in the rear ranks", as it were, was GI Joe.

Dave Oesterreich