"Metal Gear Solid: Portable Ops (メタルギアソリッド ポータブルオプス, Metaru Gia Soriddo Potaburu Opusu?) (commonly abbreviated to MPO) is a stealth game directed by Masahiro Yamamoto and written by Gakuto Mikumo, with series creator Hideo Kojima acting as a producer. Portable Ops was developed by Kojima Productions and published by Konami in 2006 for the PlayStation Portable. It is the third Metal Gear title for the PSP and the first one to retain the series' action-based gameplay. It is also the first canonical outing of the Metal Gear Solid series for a portable platform, following the storyline of Metal Gear Solid 3: Snake Eater.
Set in 1970 in South America, six years after the events of Snake Eater, the game follows the exploits of Naked Snake after his former unit, FOX, goes renegade.  The game also chronicles the eventual founding of FOXHOUND and The Patriots, as well as the inspiration of the military state Outer Heaven."
Source: Wikipedia, "Metal_Gear_Solid:_Portable_Ops," available under the CC-BY-SA License.