In September of 1939, Germany and Russia invaded Poland, and the European war became inevitable.  Unlike the Great War where Equestria remained mostly neutral, this time there will be no safe harbor for the small nation of ponies.  While they quietly attempt to withdraw their citizens from the bonfire that is engulfing Europe, they are operating blind.  There is a fair chance their peacetime ally of Germany has already decided Equestria would make a good base for an attack on America, and just as likely the Americans will move to prevent it, resulting in the war arriving on Equestria’s shore regardless of any futile attempt at neutrality between the Great Powers.

Celestia has to do something to stop this disaster, or at least mitigate the destruction to save her little ponies from the ravages of war.  If only there were some way to read Germany’s mail so Equestria could remain one step ahead of them.  With Cadence on a last-ditch diplomatic mission to France and Celestia distracted by other affairs of state, the crushing responsibility falls on the thin shoulders of a young unicorn researcher and a reluctant spy.  Together, they will carry out a daring raid right into the underwater clutches of a German submarine and try to escape without getting caught or killed.

While on the moon, dark forces have begun to stir…

Art by Airy Words and a certain amount of AI and tweaking, but mostly Airy Words
Editing by Tek, Airy Words, and whoever finds the inevitable typo and politely reports it.
Credit to DC Comics and the 1970s series Weird War Tales, of which I have several in my basement collection.