From a 2006 article in Der Speigel.
SPIEGEL: You yourself fought against the Nazis in Europe in 1945 and came to Berlin just after the end of the war and stayed there for eight months. Could you still feel much of a Hitler reverence?Remember, without Mel, there would not be this.
Brooks: Everywhere you went you could sense a great relief that the war was finally over. I myself was shaken by the extent of the destruction. When we were transporting away a few prisoners of war in a train, I discovered an old man who looked like my grandfather. He suddenly leaped out of the carriage. I took my rifle and aimed at him. He called (Brooks says in German): "Don’t shoot, I have to shit". Most of the Germans who survived the war were just poor simple people.
As for his service - he wasn't making movies.
Military service: US Army (WWII, Cpl.)Mench.
Mel Brooks joined the Army when he was 17, became a combat engineer, where one of his tasks was defusing landmines. Brooks fought at the Battle of the Bulge.