[a] The USMC has a long history of cooperation with the U.S. Department of State, which administers the nation's diplomatic posts; Marines have served on special missions as couriers, guards for embassies and delegations, and security for U.S. citizens in the frontier.

Notable examples include engagements at Derna and Tripoli, the secret mission of Archibald H. Gillespie in the Mexican-American War, and actions during the Boxer Rebellion.

In response to the 2012 Benghazi attack, Congress ordered a near doubling of Marine Security Guards in the midst of a post-war drawdown in overall USMC numbers.

Marine Security Guards also provide protection for personnel and classified material located within designated diplomatic missions.

[2] Headquarters Company, along with MSG School, is composed of approximately 100 Marines providing administrative, logistical, legal, training and education support.

Marines of any Military Occupational Specialty may volunteer for a three-year tour of duty;[11] however, non-Staff NCOs with dependents are not eligible, as well as Marines with potentially offensive tattoos, legal or security restrictions, non–United States citizenship, dual citizenship, significant financial indiscretions, and any other restriction that would prevent a top secret clearance.

This article incorporates public domain material from websites or documents of the United States Marine Corps.