Conflict with Diamond Dogs
When OE captured a coltan mine in southern Africa, Diamond Dogs was hired to retake it in order to prevent its resources being depleted. OE later attempted to assassinate the president of a South American country, at the behest of various disgruntled generals opposed to the president's democratic reforms. Despite OE's use of snipers and covert strike squads, Diamond Dogs foiled the assassination attempt by providing a truck escort to protect the president.
A port in the Western Sahara was later occupied by OE, causing a pro-independence group in the area to hire Diamond Dogs to drive them out. During this time, their equipment had drastically improved, implying that someone was supplying them with cutting edge technology on the side, which required Diamond Dogs to bring along an armored vehicle.
In West Asia, OE attempted to destroy a pipeline via sabotage, with Diamond Dogs again hired to drive them out. Diamond Dogs' Intel Unit suspected that they were backed by Cipher, which alongside OE's cutting edge equipment required them to use a Walker Gear.
Eventually, using its oil-based rights to gain cutting-edge technology and a sizable force, OE was hired by a rebel guerrilla group to occupy a West African oil facility before Diamond Dogs drove them out. This required Diamond Dogs to utilize their then-recently completed Battle Gear as well as two Walker Gears.
OE had a contract for oilfields in the Saudi Arabia peninsula, but after it was denied, they conducted a coup d'état in a mountainous nation and took over its government and broadcasting system. Diamond Dogs was forced to intervene, and with the use of the Battle Gear and three Walker Gears, waged total war on OE and wiped the group out for good.
Behind the scenes
OE is mentioned as the opposing group in several Key Dispatch Missions in Metal Gear Solid V: The Phantom Pain, specifically the third (Recapture the Coltan Mine), seventh (Presidential Escort), twelfth (Recapture the Port Facilities), fifteenth (Defend the Pipeline) eighteenth (Recapture the Oil Facility) and final (Prevent the Coup d'état) missions.
- Metal Gear Solid V: The Phantom Pain (mentioned)