When my friend first told me about "Der Eisendrachen," I thought it meant the "iron kite" (in German "der Drachen" can refer to a kite). Needless to say, I was a little confused. Haha. Anyways, I postulate that maybe Die Festung Hohenwerfen (the Austrian fortress where this map appears to be located), may have some connection to Group 935. Perhaps it was a place to securely research the making of wonder weapons. The reason I say this is because Der Riese was a facility which built wonder weapons with the name of another mythical creature (The Giant). I wouldn't be surprised if a new 1940's-esque wonder weapon comes into play (or even the reintroduction of the Wunderwaffe DG-2). Maybe "Der Eisendrachen" refers to this new weapon (it could be a gun, vehicle, or maybe even a cannon or bomb of sorts).