At the end of World War II, the once-isolationist American Catholic Church appointed ‘consultants’ to the U.S. delegation to the 1945 United Nations Conference on International Organization at San Francisco (UNCIO), a parley which had been mandated by the Big Three to draft a charter for the projected world organization. This analysis, based primarily on archival sources from the U.S. State Department, the National Catholic Welfare Conference (NCWC), and the Catholic Association for International Peace (CAIP), focuses on the bid by these international affairs specialists from the NCWC and the CAIP to modify the Dumbarton Oaks and Yalta proposals along the lines suggested by Pius XII’s ‘Five Point Peace Program’ and the American hierarchy’s statements, On International Order and On Organizing World Peace. In this crusade to ‘liberalize’ the UN Charter, this study proposes, the American Catholic Church realized only partial success. This limited accomplishment was, nevertheless, sufficient impetus for its progression from public hostility to cautious promotion of the UN. Co-published with Catholic University, Department of Church History.