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.

The 511th PIR was formed at Camp Toccoa, GA, in January 1943 and in March transferred to Camp Mackall, NC before heading to Fort Benning, GA, battalion by battalion for jump training. After the difficulties encountered by Allied airborne operations during Operation Husky in July 1943, from 6–10 December the 511th PIR took part in the successful Knollwood Maneuver that secured the future of American airborne units. After final examination at Camp Polk, LA, the regiment proceeded to Camp Stoneman, CA, and in May 1944 embarked for the Pacific on the troop transport SS Sea Pike. It trained at Oro-Dobodura in New Guinea until November 1944, when it was sent to the Philippines to join the Battle of Leyte.