Starfleet Security was founded in the spring of 2137 in order to provide a security force for Starfleet Headquarters.  The initial membership of Starfleet Security comprised fourteen members of Military Assault Command Operations who were granted transfers into Starfleet per Starfleet Administration Order #15.  Starfleet Security was briefly located at UESPA headquarters before relocating to Starfleet Headquarters, along with all other Earth Starfleet offices, in the summer of 2137.  By the end of 2139, the office had been expanded considerably, with the Director of Starfleet Security promoted from Commander to Captain.