As per the etymology for "dry run", I wonder if the roots to its artillery past aren't stronger than what is given on the site... When muzzle-loading cannon is fired, the bore is swabbed out with a wet sponge on a pole so that the embers from the shot that was fired, do not prematurely ignite the gunpowder that is being loaded for the next shot. Of course, if the exercise is just a drill, there would be no need for a wet sponge. A dry one would be used. Hence, "dry run"?