| Unit Name: | Anti-Terrorism Battalion (AT BN) |
| Dates: | 2002–2007 (USMC) 2007–2013 (USMCR) |
| Country: | United States of America |
| Branch: | United States Marine Corps |
| Type: | Specialized Infantry |
| Size: | 1,000 |
| Garrison: | Marine Corps Base Camp Lejeune |
| Motto: | Vigilia Aeternus (Eternal Vigilance) |
| Battles: |
The United States Marine Corps' Anti-Terrorism Battalion (AT BN) was a specialized infantry battalion. The battalion was disbanded in 2013.
In response to the 9-11 attacks, the mission of the Anti-Terrorism Battalion was to rapidly deploy specially trained advanced infantry, intelligence personnel, support elements, and sustainable forces to detect, deter, defend, and conduct initial incident response to combat the threat of terrorism worldwide.
After September 11, 2001, the Marine Corps began rotating standard infantry battalions such as 3rd Battalion 8th Marines (3/8) through 6-month on-call assignments as the designated "Anti-Terrorism Battalion" to meet short term/no-notice mission requirements. Examples included augmenting security at the American Embassy in Kabul, Afghanistan, with a rifle company for site security. These rotations required company and smaller size detachments but removed the entire force of the 1,000-man infantry battalion from the main war fighting effort. This posed a problem for the Marine Corps as Operations Enduring Freedom (OEF) and Iraqi Freedom (OIF) began to require additional full strength infantry battalions to rotate in and out of theater at a higher rate.
The permanent AT Battalion (AT BN) was activated 29 August. 2001, under the 4th Marine Expeditionary Brigade (Anti Terrorism) (4th MEB (AT)). The 4th MEB (AT) was deactivated in February 2006, on the same day Marine Corps Forces Special Operations Command stood up, and the AT BN was administratively transferred initially to the II Marine Expeditionary Force (II MEF), and then finally to the 2d Marine Division by March 2006. The Foreign Military Training Unit (FMTU) along with 4th MEB (AT BN) headquarters element were absorbed into Marine Corps Special Operations Command (MarSoc).
The AT BN initially consisted of;
Between 2004 and 2007, the AT Battalion had served in western Al Anbar, central Baghdad and northern Diyala provinces of Iraq. Deployments included:
Numerous Marines also augmented other requirements for National Police Training Teams (NPTT), Military Transition Teams (MiTTs), and MEF augmentation requests to other infantry units.
Most Marines in the battalion completed two to three consecutive combat deployments in a single three-year tour of duty with the battalion as part of their initial 4-year enlistment contract.
On 13 July 2007, the active duty AT BN stood down in name and was reflagged as the 2nd Battalion 9th Marines as part of the increase in the size of the Marine Corps.
In 2007 the Marine Corps Reserve reactivated the AT BN to meet similar mission requirements for the 4th Marine Division that the active duty battalion had met.
Fox Company AT BN 4th MARDIV augmented the US Embassy security and Anti-Terrorism operations in Sana'a Yemen 2011–2012.
On 21 September 2013, the USMCR AT BN was officially deactivated.