Further contributions are always welcome but the answer of /u/Domini_canes to [What role did the Vatican City play during WWII?] (https://www.reddit.com/r/AskHistorians/comments/3fpb6s/what_role_did_the_vatican_city_play_during_wwii/), including a couple of links to other posts about the role of Pius XII, may be a good place to start.