Half-Life: Opposing Force (commonly referred to as OpFor or Op4) is a critically acclaimed expansion pack for Half-Life, developed by Gearbox Software and released by Sierra On-Line on November 18, 1999.
In Opposing Force, the player returns to Black Mesa as Corporal Adrian Shephard, one of the soldiers sent in to eliminate the civilians from the original game. On an undisclosed mission to Black Mesa, things don't quite go as planned, and Shephard gets separated from his unit at the beginning of the game.
Now alone and without any orders, Shephard must face not only a new alien threat, but also the government agents sent in after the soldiers pull out. Their mission is to cover up the incident by destroying the facility and eliminating everything on their way, including the soldiers who were left behind.
In the single-player campaign, some of these weapons replace their Half-Life counterparts (Desert Eagle - .357 Magnum, M40A1 - Crossbow, Pipe wrench/Combat knife - Crowbar, Shock Roach - Hivehand). However, in the multiplayer game the player can carry both the new Opposing Force weapons and their Half-Life variants at the same time, while cheat codes also make it possible to possess and use these weapons in single-player mode.
Half-Life: Opposing Force was announced on April 15, 1999 to be developed by Gearbox Software. At the time, Gearbox was a new company formed by the core members of the defunct Rebel Boat Rocker which had been shut down after a struggle with their publisher on their first video game project. The team wanted to work on small scale titles based on an existing technology rather than creating a completely new game.
Meanwhile, Valve was busy with developing Half-Life 2 and its supporting engine technology. They were looking for someone to take over their role and expand the Half-Life universe so they could focus on their future titles. Gearbox had connections at Valve and were interested in meeting them to see what they could put together. However, Gabe Newell ended up calling them first as he a similar idea for a project. Through their connections, Gabe was told what Gearbox was doing, and he believed they'd be a good fit. Both companies got together to discuss and explore the possibilities.
Randy Pitchford pitched the idea of player returning to Black Mesa as one of the soldiers invading the facility occurring during the same time as the events of Half-Life, retelling the story from another character's perspective. He likened the concept to the play Rosencrantz and Guildenstern Are Dead. Newell, inspired by The Alexandria Quartet series of novels, also wanted to have a Rashomon-esque structure and allow the players to experience the same events from a different point of view. The deal was signed, and the production of the Opposing Force expansion pack went forward.
- The demo version was released after the game's release on March 4, 2000. It is featuring portions of Welcome to Black Mesa, Friendly Fire, Foxtrot Uniform with minor changes.
- Several areas of the chapter Pit Worm's Nest bear a striking resemblance to the trash compactor from Star Wars (1997), particularly the pattern of red lights above their exit doors.
- The chapter name Foxtrot Uniform is derived from the NATO phonetic alphabet, referring to letters "F" and "U". It is a military euphemism for "fucked up," sometimes preceded by "Alpha" (for "all", represented by "A").
- If the player follows Gordon Freeman through the portal to Xen in We Are Not Alone, the game will end, accusing the player of trying to rewrite the history with a game over message that says: "Evaluation terminated, Subject attempted to create a temporal paradox". This means what happened in the original level was changed by the player.
Original installation splash screen.
The commander talking over the radio.
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