The 511th Parachute Infantry Regiment (511th PIR) was an airborne infantry regiment of the United States Army, first activated during World War II under Colonel Orin D. "Hard Rock" Haugen. It formed the parachute infantry element of the 11th Airborne Division. The full history of the regiment is the subject of the book, When Angels Fall: From Toccoa to Tokyo, the 511th Parachute Infantry Regiment in World War II (2019) by author and historian Jeremy C. Holm whose grandfather served in the regiment's Company D during the war.