1. An Ahnenerbe expedition to "prove" that Çatal Hüyük (one of the earliest known cities, sited in southwestern Turkey) or some other made-up city if your players are geography nitpickers was in fact an Aryan civilization. Could also have various lost artifacts of power involved. Maybe they're trying to forge an Aryan origin as grounds for a casus belli to invade Turkey (when what they really want is to control the Straits of Bosphorus and open up a new theater against the Soviets).
2. Searching for a gateway to the underground advanced civilization mentioned in Edward Bulwer-Lytton's
The Coming Race, so that they can discover the secret of Vril and develop Vril-powered aircraft and tanks. For shits and giggles, add in the
Black Sun Society. Double points if you work in a "It was a dark and stormy night" reference.
3. They're attempting to find a lost fortress of the Teutonic Knights from the 13th century (yes, the Teutonic Knights were present in the Crusades and had castles in Armenia/eastern Turkey) where a band of the Knight's strongest warriors are said to lie buried under a magical spell that would allow them to rise again. Or alternately, the Nazis have discovered some kind of magic or science to raise them from the dead (Nazi Zombie Knights HO!) and are just trying to find the castle and then the catacombs.