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September 11 Chronology

DHS and its many partners across the federal government, public and private sectors, and communities across the country and around the world have worked since 9/11 to build a new homeland security enterprise.

Below we've laid out some of the concrete measures that have been put in place since 9/11.

Early 1999

Lead up to 9/11: Osama Bin Laden summoned operatives to Afghanistan to discuss using commercial aircraft as weapons and developed a list of potential targets in the United States.


Today, in concert with public and private sector partners as well as international allies, this Administration has developed a multi-layered information sharing security strategy to target and identify both known and unknown individuals that may pose a threat to the United States wherever the operational planning might occur with the goal of preventing such persons from entering the country.

April 1999

Lead up to 9/11: The hijackers began to obtain passports and visas for travel to the United States.


DHS and other federal partners have built a capacity to more extensively vet those individuals applying for visas or travel to the U.S.

For example, through the Visa Security Program, which did not exist on 9/11 and is now operational at 19 posts in 15 countries, Immigration and Customs Enforcement, in conjunction with the State Department, deploys trained special agents overseas to high-risk visa activity posts to conduct targeted, in-depth reviews of particular visa applications and applicants before they reach the United States.

1999 and 2001

Lead up to 9/11: Many of the hijackers prepared for the 9/11 attack while living in Germany.


The Department of Homeland Security (DHS), in collaboration with the Departments of Justice and State, has signed Preventing and Combating Serious Crime Agreements with 18 countries, including Germany, to share information about terrorists and criminals.

April 2001

Lead up to 9/11: The hijackers began arriving in the U.S. on tourist visas with cash and travelers checks acquired in the Middle East.


DHS partners with the Terrorist Screening Center, the National Counterterrorism Center and other federal entities to analyze travel-related data in order to better understand and anticipate the travel patterns of known or suspected terrorists.

Today’s travel related databases along with threat-related intelligence have been essential in identifying, targeting, and interdicting known and suspected terrorists as well as suspicious cargo before it enters the United States.


Lead up to 9/11: The hijackers enrolled in flight schools and conducted cross-country surveillance flights in order to identify aircraft that would produce their desired impact.


The Transportation Security Administration (TSA) has responsibility for ensuring that foreign students seeking training at flight schools do not pose a threat to aviation or national security. TSA performs background checks, including government watchlist matching, a criminal history check, and an immigration status check.


Lead up to 9/11: Several of the hijackers were apprehended by U.S. law enforcement for various traffic violations.


Today, fusion centers throughout the country serve as focal points at the state and local level for the receipt, analysis, gathering, and sharing of threat and vulnerability-related information.

In addition, the Nationwide Suspicious Activity Reporting Initiative helps to train state and local law enforcement to recognize behaviors and indicators related to terrorism, crime and other threats while standardizing how those observations are analyzed and disseminated.

Finally, state and local law enforcement officers can determine whether an individual is on a watchlist through the National Crime Information Center.

September 11, 2001

Lead up to 9/11: The hijackers passed through security checkpoints at four U.S. airports, allegedly carrying knives, box cutters and concealed weapons on their person or in carry-on luggage.


Multilayered security measures are now in place to enhance aviation security including the prescreening of passengers; the deployment of new technologies; and training of airport security and law enforcement personnel to better detect behaviors associated with terrorism.

Since 9/11, the capacity of frontline security personnel and new technologies has significantly expanded. Through Secure Flight, DHS now prescreens 100% of the 14 million passengers flying weekly to, from, and within the U.S. against government watchlists. In addition, all checked and carry-on baggage is now screened for metallic and non-metallic threats by new technologies as well as over 52,000 transportation security officers at more than 450 airports across the country.

September 11, 2001

Lead up to 9/11: Eight of the hijackers were randomly selected for additional screening and a gate agent flagged two as suspicious, none were prevented from boarding their flights on 9/11.


Today, TSA’s Behavior Detection Officers utilize non-intrusive behavior observation and analysis techniques to identify potentially high-risk passengers who exhibit behaviors that indicate they may be a threat to aviation and/or transportation security and refer them for additional screening.

TSA also conducts screening of passengers at boarding gates based on current intelligence and passengers of interest.

September 11, 2001, 8:19AM

Lead up to 9/11: Flight attendants and passengers began reporting hijackings of the aircraft via airphone.


Following 9/11, all commercial aircraft have been secured through the hardening of cockpit doors. In addition, the risk-based deployment of Federal Air Marshals, the Federal Flight Deck Officer program, in which eligible flight crewmembers are authorized by TSA to use firearms to defend against violence, and the crewmember behavior recognition and response training program, all provide additional layers of aviation security.

September 11, 2001

Lead up to 9/11: Air traffic control operators, military personnel and first responders on the ground lacked situational awareness of what other agencies were doing to address the developing crisis.


Through the use of mobile and fixed site technologies, voice radio systems used by first responders are more interoperable than ever before. Since 9/11, the federal government has made significant organizational changes and investments in training and technical assistance to improve emergency communications capabilities.

Moreover, the National Emergency Communications Plan and Incident Command System have established standardized plans, protocols, and procedures to improve command, control, and communications.

Read the Implementing 9/11 Commission Recommendations, Progress Report 2011

Last Updated: 01/10/2022
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