The idea of such an attack was well known [and] had been
wargamed as a possibility in exercises before September 11.
- Professor John Arquilla of the Naval Postgraduate
School, Monterey, California
Yet these claims were untrue. Not only had the U.S. military and other government agencies discussed the possibility of such attacks, they also conducted numerous training exercises in the year or two before September 11 based around scenarios remarkably similar to what occurred on 9/11. As John Arquilla, a professor of defense analysis at the Naval Postgraduate School in Monterey, California, said, "No one knew specifically that 20 people would hijack four airliners and use them for suicide attacks against major buildings ... but the idea of such an attack was well known [and] had been wargamed as a possibility in exercises before September 11." 
The existence of these training exercises proves that official claims that the events of September 11 were unimaginable have been false. However, future investigations of 9/11 will need to determine whether these exercises served a more nefarious purpose. For example, might they have been intended as a smokescreen for rogue individuals working within the military and other government agencies who were involved in planning the attacks? Thus, if colleagues overheard these individuals discussing matters such as planes hitting the World Trade Center or crashing into the Pentagon, they could have claimed they were simply talking about a forthcoming training exercise.
The following summary outlines three specific categories of training exercises and preparations that took place before September 11. Firstly, those that dealt with terrorists deliberately crashing a plane into the World Trade Center. Secondly, those that considered an aircraft crashing into the Pentagon. And thirdly, those that resembled other aspects of the 9/11 attacks, such as the use of planes as weapons more generally.
1) PREPARING FOR AN ATTACK ON THE WORLD TRADE CENTER
i) Military Personnel Briefed on Possible Attack on the WTC
At some point before 9/11, members of staff at NORAD's Northeast Air Defense Sector (NEADS) in Rome, New York appear to have been briefed on the possibility of terrorists deliberately crashing a plane into the World Trade Center. In her book Touching History: The Untold Story of the Drama that Unfolded in the Skies Over America on 9/11, author Lynn Spencer described the actions of Trey Murphy, a former Marine who on September 11 was a weapons controller at NEADS. Murphy learned of the first plane hitting the WTC while still at home. According to Spencer: "The news brought to mind one of his briefings: What if a terrorist flies an airplane with a weapon of mass destruction into the World Trade Center? It had always been one of the military's big fears." She added, "The image on the [television] screen certainly reminded him of his briefing." 
ii) NORAD Trains for Terrorists Crashing a Hijacked Plane into the WTC
At unspecified times during the two years prior to September 11, the North American Aerospace Defense Command (NORAD, the military organization responsible for defending U.S. airspace) conducted training exercises that simulated hijacked aircraft being deliberately crashed into targets so as to cause mass casualties. As USA Today later reported, "One of the imagined targets was the World Trade Center." NORAD stated that "Numerous types of civilian and military aircraft were used as mock hijacked aircraft" in these exercises. Among other things, the exercises tested "track detection and identification" (presumably on military radar screens); "scramble and interception" by fighter jet planes; and "hijack procedures." According to NORAD, the exercises were regional drills, not regularly scheduled continent-wide exercises, and unlike what happened on 9/11, the planes in the simulated scenarios were coming from a foreign country rather than from within the United States. 
NORAD added that, before 9/11, "At the NORAD headquarters' level we normally conducted four major exercises a year, most of which included a hijack scenario."  Shortly after September 11, the New Yorker similarly reported, "During the last several years, the government regularly planned for and simulated terrorist attacks, including scenarios that involved multiple-plane hijackings." 
In spite of these specific concerns and preparations, the 9/11 Commission Report claimed that NORAD was "unprepared for the type of attacks launched against the United States on September 11, 2001. [It] struggled, under difficult circumstances, to improvise a homeland defense against an unprecedented challenge [it] had never before encountered and had never trained to meet." 
2) PREPARING FOR A PLANE HITTING THE PENTAGON
The number of training exercises based around a plane crashing into the Pentagon is particularly notable. In the 12 months prior to 9/11, we know of three such exercises that were conducted, and a fourth exercise that considered, but rejected, this scenario.
i) The Pentagon Mass Casualty Exercise
Between October 24 and October 26, 2000, emergency responders gathered at the Office of the Secretary of Defense conference room in the Pentagon for the Pentagon Mass Casualty Exercise. Responses to several scenarios were rehearsed, including the possibility of a passenger aircraft crashing into the Pentagon. A military news service described the exercise: "The fire and smoke from the downed passenger aircraft billows from the Pentagon courtyard. Defense Protective Services Police seal the crash sight. Army medics, nurses, and doctors scramble to organize aid. An Arlington Fire Department chief dispatches his equipment to the affected areas." It sounds almost like a description of what happened on September 11. But then "Don Abbott, of Command Emergency Response Training, walks over to the Pentagon and extinguishes the flames. The Pentagon was a model and the 'plane crash' was a simulated one." 
ii) Medics Practice for a Plane Hitting the Pentagon
Little over six months later, in May 2001, the U.S. Army's DiLorenzo Tricare Health Clinic and the Air Force Flight Medicine Clinic--which are both located within the Pentagon--along with Arlington County Emergency Medical Services, held a tabletop exercise. The scenario they practiced for was an airplane crashing into the Pentagon's west side--the same side as was hit on September 11.  There have been some contradictions between reports, regarding the exact details of this exercise. But according to U.S. Medicine newspaper, the plane in the scenario was a hijacked Boeing 757, the same kind of aircraft as allegedly hit the Pentagon on 9/11.  The Defense Department's book about the Pentagon attack, Pentagon 9/11, reported that the plane in the exercise scenario was a twin-engine aircraft (Boeing 757s are twin-engine aircraft), but that it crashed into the Pentagon by accident, rather than as a consequence of a hijacking.  The commanders of the two Pentagon clinics that participated later said this exercise "prepared them well to respond" to the attack on 9/11.  And Air Force Surgeon General Paul Carlton Jr. commented, "We learned a lot from that exercise and applied those lessons to September 11." 
iii) Practice Evacuation Conducted in Response to Simulation of a Plane Hitting the Pentagon
Just one month before September 11, a third plane-into-Pentagon training exercise was held. General Lance Lord, the assistant vice chief of staff of the Air Force, later recalled his experiences of 9/11, commenting, "Fortunately, we had practiced an evacuation of the building during a mass casualty exercise just a month earlier, so our assembly points were fresh in our minds." He added, "Purely a coincidence, the scenario for that exercise included a plane hitting the building." 
iv) Military Considers, but Rejects, Exercise Scenario of a Hijacked Plane Being Crashed into the Pentagon
For another exercise, military planners actually considered the possibility of a commercial aircraft being hijacked by terrorists and then crashed into the Pentagon.  From April 17-26, 2001, the U.S. Joint Chiefs of Staff conducted the exercise Positive Force 01, which was designed "to test, evaluate, and train the national defense community in decision making and execution of mobilization and force deployment in response to multiple crises."  Positive Force was a "continuity of operations exercise," dealing with government contingency plans to keep working in the event of an attack on the U.S.  NORAD was one of the agencies invited to participate. 
During the planning of this exercise, special operations officers had to think like terrorists and plot unexpected attacks that would test NORAD's air defenses. According to an officer who was temporarily assigned to NORAD in the spring of 2001, "the NORAD exercise developers wanted an event having a terrorist group hijack a commercial airline and fly it into the Pentagon."  The NORAD employee who suggested this had been asked for a scenario in which the Pentagon was rendered inoperable and part of its functions had to be moved to another location.  However, the U.S. Pacific Command didn't want the scenario, "because it would take attention away from their exercise objectives." Joint Staff action officers then rejected the scenario as being "too unrealistic." 
3) OTHER PREPARATIONS AND EXERCISES
There were other training exercises and emergency preparations that are noteworthy. Few specific details have been disclosed of these. They have not been reported to have included scenarios of aircraft hitting the World Trade Center or Pentagon, but they relate to what happened on 9/11 in other ways.
i) Department of Transportation Exercise Involves a Cell Phone Call from a Hijacked Plane
Less than two weeks before September 11, on August 30, 2001, an exercise was held at the Department of Transportation in Washington, DC, as part of its preparations for the 2002 Winter Olympics. According to Ellen Engleman, the administrator of the DOT's Research and Special Programs Administration, this was a "full intermodal exercise" (although she did not explain what exactly that meant). Engleman has recalled: "During that exercise, part of the scenario, interestingly enough, involved a potentially hijacked plane and someone calling on a cell phone, among other aspects of the scenario that were very strange when 12 days later, as you know, we had the actual event [of 9/11]."  (As has been widely reported, numerous passengers on the hijacked planes allegedly were able to make calls using cell phones to people on the ground.) The Department of Transportation was subsequently much involved in the emergency response on September 11, with its Crisis Management Center being activated less than 30 minutes after the first attack on the WTC. 
Although further details of this exercise are unknown, the fact that Engleman referred to "other aspects of the scenario that were very strange" indicates that it resembled the 9/11 attacks in other ways.
ii) Threat of Planes as Weapons Considered During Preparations for 'Special Security Events'
The possibility of attacks resembling those that occurred on 9/11 was considered during the preparations for what are called "National Special Security Events" (NSSEs). This is particularly notable, since preparations were underway in the two cities targeted in the attacks--New York and Washington--the morning of September 11, for National Special Security Events due to take plane later that month. Considering that only four or five events per year were being designated as NSSEs, it seems hard to dismiss this as just coincidence.
Since 1998, the National Security Council has had the authority to designate any important upcoming public event as an NSSE.  Events such as the 2000 Republican and Democratic National Conventions and the 2000 presidential inauguration were designated as NSSEs.  Once an event has been designated as an NSSE, the Secret Service becomes the lead agency for designing and implementing its security plan, while the FBI and FEMA also have major security roles. 
According to the Secret Service, there would be "a tremendous amount of advance planning and coordination" for NSSEs. A variety of training initiatives would be conducted, including "simulated attacks and medical emergencies, inter-agency tabletop exercises, and field exercises."  Most significantly, according to Louis Freeh, the director of the FBI from September 1993 to June 2001, in the years 2000 and 2001, the subject of "planes as weapons" was always one of the considerations in the planning of security for "a series of these, as we call them, special events." Freeh told the 9/11 Commission that "resources were actually designated to deal with that particular threat," and confirmed that "the use of airplanes, either packed with explosives or otherwise, in suicide missions" was "part of the planning" for NSSEs.  Although Freeh did not state it, it seems a quite likely possibility that the "simulated attacks ... inter-agency tabletop exercises, and field exercises" held during 2000 and 2001 in preparation for NSSEs would therefore have included the scenario of planes being used as weapons.
Furthermore, the morning of September 11, Secret Service employees in New York were "about to attend meetings to prepare for the upcoming meeting of the United Nations General Assembly."  An additional 100 Secret Service employees were in New York to help prepare for the event.  The General Assembly's annual gathering of world leaders was scheduled for September 24 to October 5, with President Bush due to give his address on September 24.  Significantly, this event was designated as an NSSE.  Since the UN's previous 'Millennium Summit' in New York in September 2000 was an NSSE, it seems logical to assume that the 2001 gathering received NSSE status before 9/11, and not simply as a result of the attacks. 
Preparations were also underway in Washington, DC on September 11 for the annual meetings of the International Monetary Fund (IMF) and the World Bank, which were scheduled to take place on September 29-30. Many of the agencies that would be involved in the emergency response to the Pentagon attack later that morning were taking part in these preparations.  It was reported several weeks before 9/11 that these meetings had been designated as an NSSE. 
The question therefore arises, might preparations for the threat of planes being used as weapons have been taking place around the time of the 9/11 attacks? Were "simulated attacks ... inter-agency tabletop exercises, and field exercises" based around planes used as weapons scheduled in New York and Washington around that period? Further research and investigation is required to answer these questions.
The above summary describes training exercises and preparations that have been reported or publicly discussed. But it seems reasonable to assume that there were other exercises held in the year or two before 9/11 that have not yet been reported and that also resembled the attacks that took place that day. If they occurred, we need to know about these other exercises and we must consider what role they might have played in the planning and execution of the September 11 attacks.
 "National Security Advisor Holds Press Briefing." White House, May 16, 2002.
 "President Addresses the Nation in Prime Time Press Conference." White House, April 13, 2004.
 Steven Komarow and Tom Squitieri, "NORAD Had Drills of Jets as Weapons." USA Today, April 18, 2004.
 Kevin Howe, "Expert Stresses Need for Intelligence." Monterey County Herald, July 18, 2002.
 Lynn Spencer, Touching History: The Untold Story of the Drama That Unfolded in the Skies Over America on 9/11. New York: Free Press, 2008, p. 179.
 Steven Komarow and Tom Squitieri, "NORAD Had Drills of Jets as Weapons."
 Barbara Starr, "NORAD Exercise Had Jet Crashing into Building." CNN, April 19, 2004.
 "September 11, 2001." New Yorker, September 24, 2001.
 9/11 Commission, The 9/11 Commission Report: Final Report of the National Commission on Terrorist Attacks Upon the United States (Authorized Edition). New York: W. W. Norton & Company, 2004, p. 45.
 Dennis Ryan, "Pentagon MASCAL Exercise Simulates Scenarios in Preparing for Emergencies." MDW News Service, November 3, 2000.
 Arlington County, Virginia, report, Titan Systems Corp., Arlington County: After-Action Report on the Response to the September 11 Terrorist Attack on the Pentagon. 2002, p. B17; Alfred Goldberg et al., Pentagon 9/11. Washington, DC: Defense Department, Office of the Secretary, Historical Office, 2007, pp. 23 and 107.
 "Crisis Response Puts Agencies on Path to Better Coordination." U.S. Medicine, January 2002.
 Alfred Goldberg et al., Pentagon 9/11, p. 107.
 Matt Mientka, "Pentagon Medics Trained for Strike." U.S. Medicine, October 2001.
 Dean E. Murphy, September 11: An Oral History. New York: Doubleday, 2002, p. 222.
 Lance Lord, "A Year ago, a Lifetime ago." Air Force Print News, September 10, 2002.
 Danielle Brian, "POGO Letter to Hon. Thomas K. Kean, Chairman, National Commission on Terrorist Attacks Upon the United States." Project On Government Oversight, April 13, 2004.
 "Positive Force." GlobalSecurity.org, June 9, 2002.
 Julian Borger, "Hijackers Fly into Pentagon? No Chance, Said Top Brass." The Guardian, April 15, 2004.
 Nicole Gaudiano, "Military Considered Hijacked Plane Exercise, and Rejected it." Air Force Times, April 13, 2004.
 Terry Ropes, "Exercise Scenario." September 18, 2001, internal e-mail; Julian Borger, "Hijackers Fly into Pentagon? No Chance, Said Top Brass."
 Nicole Gaudiano, "Military Considered Hijacked Plane Exercise, and Rejected it."
 Terry Ropes, "Exercise Scenario"; Julian Borger, "Hijackers Fly into Pentagon? No Chance, Said Top Brass."
 Mineta Transportation Institute, National Transportation Security Summit, Washington, DC. San Jose, CA: Mineta Transportation Institute, October 30, 2001, p. 108.
 Senate Committee on Commerce, Science, and Transportation, Federal Aviation Security Standards. 107th Cong., 1st sess., September 20, 2001; Senate Committee on Commerce, Science, and Transportation, Statement of Ellen G. Engleman, Administrator, Research and Special Programs Administration, U.S. Department of Transportation. 107th Cong., 1st sess., October 10, 2001.
 Bruce M. Lawlor, "Military Support of Civil Authorities: A New Focus for a New Millennium." Journal of Homeland Defense, October 2000; "National Special Security Events." United States Secret Service, 2002.
 "National Special Security Events Fact Sheet." U.S. Department of Homeland Security, July 9, 2003; "Fact Sheet: 2005 Presidential Inauguration: National Special Security Event." U.S. Department of Homeland Security, November 8, 2004.
 "National Special Security Events Fact Sheet"; Sarah D. Scalet, "In Depth: Democratic Party Convention Security." CSO, September 2004.
 "National Special Security Events."
 National Commission on Terrorist Attacks Upon the United States: Tenth Public Hearing. 9/11 Commission, April 13, 2004.
 United States Congress, Honoring United States Secret Service New York Field Office for Extraordinary Performance During and Immediately Following September 11, 2001. 107th Cong., 2nd sess., April 23, 2002.
 "Spotlight on: Barbara Riggs." PCCW Newsletter, Spring 2006.
 "UN General Security Council Condemns Attacks." Reuters, September 12, 2001; "Bush to Attend UN General Assembly." Associated Press, October 29, 2001.
 Al Baker, "Security Tight for Start of United Nations Meeting in New York." New York Times, November 10, 2001; House Committee on the Judiciary, Proposal to Create a Department of Homeland Security. 107th Cong., 2nd sess., July 9, 2002; "National Special Security Events Fact Sheet."
 U.S. Department of the Treasury, Program Performance Report Fiscal Year 2000. Washington, DC: U.S. Department of the Treasury, 2000, p. 177; United States Congress, Making Appropriations for Military Construction, Family Housing, and Base Realignment and Closure for the Department of Defense for the Fiscal Year Ending September 30, 2001, and for Other Purposes. Washington, DC: U.S. Government Printing Office, June 29, 2000; "Preparing for the World: Homeland Security and Winter Olympics." White House, January 10, 2002.
 Arlington County, After-Action Report on the Response to the September 11 Terrorist Attack on the Pentagon, p. A4; 9/11 Commission, The 9/11 Commission Report, p. 314.
 "Washington is Seeking Support to Handle Protests at 2 Meetings." New York Times, August 18, 2001.