My Grandfather's Involvment in WWII

I saw my grandparents over Thanksgiving break and while I was visiting them, my grandpa showed me a picture of a veteran's day reunion of his platoon or troop or whatever its called. He also showed me a picture of himself in a military uniform. My grandpa can't hear very well, so I asked my grandma if he ever talked about the war. According to her, he avoided the topic whenever someone asked him for details or specifics about his time in the army. I know that he was drafted when he was 19, and that he was an engineer. Specifically, his job was to find clean water before the rest of the troops came in. My grandma has told me that while he was in Europe, the house he was staying in was bombed; he was fortunate enough to not be in house at the time that this happened. She also said that he was promoted at some point, but she is unsure about details with that because that was something he didn't talk about.
 I never really thought much about his experience in the war, but then I found out something that sparked me interest. A man that was in my grandpa's military group (whatever it's called), who was also a friend of my grandpa's, was captured by the Germans and taken as a POW. He survived and now has a book out about his time with the Germans. I intend on finding this book and reading it and finding out more about my grandpa's involvement in the war.
My mom told me that my grandpa was also in the group of soldiers that released Jews from the concentration camps and death camps after the war. It must have been pretty awful if he so utterly refuses to talk about his experiences.
While my grandma was talking to me about this that day, she also mentioned that she still has her ration book from during the war and that I could bring it in if the class was interested in seeing it.

My dad's second wife's step-dad (I know, confusing relationship) was also in WWII. He was a paratrooper and told me a story once of how he got stuck in a tree and could do nothing but hang there while the Germans all shot up at him. Miraculously, he cut himself down though and escaped. He also managed to learn a lot of German during the war and would often say random phrases to me in German.