# September 11 Attacks **Entity class:** Terrorist attack and institutional phase transition ## Definition The **September 11 attacks** were the coordinated al-Qaeda hijackings and suicide attacks of September 11, 2001, against the World Trade Center, the Pentagon, and the attempted fourth target prevented when Flight 93 crashed in Pennsylvania. They killed nearly three thousand people and produced a durable reorganization of U.S. intelligence, aviation security, military operations, homeland security, watchlisting, information sharing, and counterterrorism. For this collection, September 11 is also a [[wiki/Zero-Day Threat Model|zero-day-like institutional exploit]]: suicide hijacking had been contemplated, but the defensive architecture had not converted that possibility into adequate doctrine, controls, training, integration, and response. ## Relationships - **official inquiry:** [[wiki/9-11 Commission|9/11 Commission]]. - **system consequences:** [[wiki/Intelligence Failure|Intelligence Failure]], [[wiki/Intelligence Integration|Intelligence Integration]], [[wiki/Aviation Security|Aviation Security]], and [[wiki/Post-9-11 Phase Transition|Post-9/11 Phase Transition]]. - **master collection:** [[collections/Terrorism, Counterterrorism, and the Intelligence Environment|Terrorism, Counterterrorism, and the Intelligence Environment]]. ## Sources / Provenance - [National Commission on Terrorist Attacks Upon the United States, *The 9/11 Commission Report*, July 22, 2004](https://www.9-11commission.gov/report/911Report.pdf). **As of:** 2026-09-23