Just a minor thing that I noticed that's worth pointing out. Field guns are large calibre mounted guns that are used in land tactical combat, particularly during WWI and WWII. The Mercury being a field gun means that it was originally used as a massive-ass sniper rifle during land combat, apparently re-purposed to fit on our airships. Interesting thought.
Field artillery are still used in modern warfare. Field pieces are not used as massive-ass sniper rifles, but generally as delivery system for shrapnel. Or, massive-ass grenade launchers. Unlike rifles which need line of sight to put lead on target, artillery pieces use over the horizon firing to put lead on target. They use massive-ass math.