Mass Casualty Exercise Horn of Africa.

GRAND BARA DESERT, Djibouti (Sept. 27, 2012) - U.S. Army Personnel Recovery Security Team members disembark a U.S. Marine Corps CH-53E Super Stallion helicopter during Mass Casualty Exercise 12-1, Sept. 25, 2012, in the Grand Bara Desert, Djibouti. The exercise followed a fictitious storyline, but called for the employment of real-world assets. While French and U.S. forces conduct frequent combined training events, this was the first exercise of this type between the two nations in Djibouti. The U.S. forces involved are assigned to Combined Joint Task Force - Horn of Africa, or CJTF-HOA. CJTF-HOA works with coalition partners, such as the French, and with countries in East Africa to promote regional security and stability. (U.S. Air Force photo by Tech Sgt. Joseph McKee)

U.S. Airmen with the 82nd Expeditionary Rescue Squadron offload an exercise participant from a U.S. Marine Corps CH-53E Super Stallion helicopter at the simulated triage site on French Forces Djibouti base, Djibouti, Sept. 25, 2012, during Mass Casualty Exercise 12-1, a joint U.S. and French medical exercise. The U.S. forces involved are assigned to Combined Joint Task Force - Horn of Africa, or CJTF-HOA. (DoD photo by Tech. Sgt. Daniel St. Pierre, U.S. Air Force/Released)21

A group of Air Force pararescuemen and an Army Site Security Team (SST) from the Kansas Army National Guard, 2nd Combined Arms Battalion, 137th Infantry Regiment, conducted a rescue mission for survivors of an aircraft crash near in Grand Bara Desert...

Army Spc. Jason Mosqueda (left) and Sgt. Darel Long, Kansas Army National Guard 2nd Combined Arms Battalion, 137th Infantry Regiment, Joint Combat Search and Rescue, provide security for an HC-130P from the 81st Expeditionary Rescue Squadron

Note:
When did the Army develop Site Security Teams?