He attended Phillips Exeter Academy and was accepted into Princeton University. Katzenbach was a junior at Princeton in 1941, enlisting right after Pearl Harbor, and served in the United States Army Air Corps in World War II. Assigned as a navigator in the 381st Bomb Squadron, 310th Bomb Group in North Africa. His B-25 Mitchell Bomber was shot down February 23, 1943, over the Mediterranean Sea off North Africa. He spent over two years as a prisoner of war in Italian and German POW camps, including Stalag Luft III, the site of the "Great Escape", which Katzenbach assisted in. He read extensively as a prisoner, and ran an informal class based on "Principles of Common Law".