Oops, Grandfather.
Even though the family was Jewish, depending on the degree of Jewishness, half and quarter Jews served in Hitler's Wehrmacht. Many lied about their Jewish history to serve, and keep their mixed-families safe. That didn't work all the time either. The enforcement of the racial laws in the ranks of the military were not consistently applied. Many times they were ignored by line officers. The book I'm reading is an amazing story based on the personal accounts, and records of about 1200 men who served. It is believed that a total of 150,000 half and quarter Jews served in the German Army, Air Force, and Navy during WWII.