Yes, you are right, it’s genitive. But “Wehrmacht” is -female-: die Wehrmacht. As for this, the genitive “der” is always used :-)
Nice poem, i have the book in german :-)
Was wondering if there was a site were you can buy a and a pieces with out having to buy the whole games.
ebay is your best bet.
Go to http://www.historicalboardgaming.com/. He ha most everything you will need or want