Since we're asking for railway guns, how bout OSS agents, or maybe commandos that we can drop behind enemy lines.
Maybe a way that a person can move around on the ground and sabotage planes, trains and automobiles.
Better yet! How bout a secret atomic weapons program for those with the mind for it? First country to develop a nuke can use it and get a reset in one big boom!
What about a Gestapo mod? or a Stalag Luft III addition? Give you a chance to torture captured pilots and then give them a chance to tunnel out?
What if we have a French resistance mod with a French family with a daughter just the right age so the downed pilot doesn't get cold while he's hiding in the barn from the Gestapo?! Knowing the AH crowd, can you imagine how many pilots would be bailing out over enemy territory to take advantage of this addition to the game?
Submarines! Thats it! Cruising the depths of the Aces High waters, sinking carriers and rescuing downed pilots!
It's all beginning to make sense to me now! The possibiliies are endless!

Dan/Slack