Tanks of the Third Reich is a military book.
While shopping at Books! Books! and Additional Books!, Homer and Marge were looking for a book in the "Martial Relations" section to improve their marriage. Meanwhile, Bart and Lisa shopped on their own. When the children returned, Homer and Marge quickly grabbed random books to pretend they were looking for something else, not for books about sex. When Bart asked his parents what they were looking at, Marge answered "Um... I'm just reading up on... artillery" as she looked at the cover.