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.
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.
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.
Fox Company AT BN 4th MARDIV augmented the US Embassy security and Anti-Terrorism operations in Sana'a Yemen 2011–2012.