This article is about a mod.
The Valve Corporation originally had plans to port Half-Life: Opposing Force into the Source engine (announced at E3 2004) much like they did with Half-Life: Source, but after an underwhelming first look at the project, the creators of Operation: Black Mesa decided it wouldn't be worth the wait. They began development in September 2007, one month before the release of Half-Life 2: Episode Two.
On December 4, 2008, the old forum website was shut down due to hackers. According to the project leader, they were not aware of the team member that had assisted in the hack. Since then, a new forum site has been launched and regained most of its former followers.
On November 2, 2009, the team released a huge media update to celebrate the 10th Anniversary of the release of the original game. Also, the project leader announced a staff expansion to aid in development.
In early 2012, the Operation: Black Mesa team merged with the Guard Duty Team to form Tripmine Studios, allowing both projects to be developed under one roof. At the same time, they publicly released an update explaining the merger.
On May 1, 2012, the team released more media from Guard Duty for the second update after the merge.
On August 21, 2012, Tripmine released both the RPG and Automatic-Turret models in a small update. .
On December 8, 2012, Tripmine released the fourth media update after the merge following their reception of Mod of the Year for 2012. 
On February 17, 2013, the team announced that both projects had received a Steam Greenlight for their eventual release. At the same time, they released more screenshots and concept art from developers. .
On April 1, 2013, further information on the Greenlight was released alongside the announcement of an upcoming trailer. .
On May 17, 2013, they released the third and final part of the concluded Greenlight media update. 
On July 29, 2013, they announced that Operation: Black Mesa was Greenlit and is awaiting the decision to be on Steam. At the same time, they updated the media to keep on the pact and the release date for the Beta Multi-Player for Project. .
On December 20, 2013, they thanked every fan for their votes for Mod of the Year 2013. At the same time, the team released another updated screenshot of the chapter "We Are Pulling Out". 
On January 16, 2017, A monthly update and media release was posted on the Tripmine Studios Forum.
On July 28, 2018, A summer update and media release detailing the studio's progress on both projects was posted on the Tripmine Studios Forum.
On June 3, 2019, Another summer update and media release gave fans a much closer look at in game weapon and character animations, as well as more 3D models and assets that will feature in the games.
On September 11, 2019, Tripmine's official YouTube channel posted a demonstration for the improved flashlight mechanic to be implemented in Guard Duty.
On January 19, 2020, Tripmine's official Youtube channel posted another demonstration for the improved Parallax Corrected Cubemaps to be implemented in the game along with Guard Duty.
A list of features planned for the final release:
- Complete re-creation of both Half-Life: Opposing Force and Half-Life: Blue Shift with expanded areas.
- Models that push the limits of the Source engine.
- New weapons.
- Multiplayer, including Deathmatch and Team Deathmatch with all the original levels fleshed out. A "capture the flag" mode may be included, but not in the initial releases.
- New voices, sounds, and visuals.
- Level design tweaks to utilize the advanced physics engine introduced in Counter Strike: Global Offensive.
- An all-new soundtrack.
- Mod DB – Top Unreleased Mod for 2007 (5th place)
- Mod DB – Honorable mention for Top Unreleased Mod for 2009
- Mod DB - Mod of the year 2010 - Players Choice (3rd Place)
- Mod DB - Honourable mention of Top Unreleased Mod of 2011 
- Mod DB - Best upcoming Mod of 2013 (1st Place) 
- ↑ http://lambdageneration.com/posts/operation-black-mesa-and-guard-duty-the-two-gearbox-expansion-remakes-join-forces-and-merge-into-one-team/
- ↑ Tripminestudios forums
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/project-relaunched-new-leader
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/unforseen-consequences1
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/ten-years-of-opposing-force
- ↑ http://www.planetphillip.com/posts/operation-black-mesa-and-guard-duty-interview/
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/operation-black-mesa-and-guard-duty-update
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/report-for-duty
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/guard-duty-and-operation-black-mesa-moty-update
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/greenlight-incoming
- ↑ http://tripminestudios.com/forum/showthread.php?tid=39
- ↑ http://tripminestudios.com/forum/showthread.php?tid=107
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/greenlight-report
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/operation-black-mesa-has-been-greenlit
- ↑ http://www.moddb.com/mods/operation-black-mesa/news/operation-thank-you
- ↑ http://tripminestudios.com/forum/showthread.php?tid=392
- ↑ Mod DB Top Unreleased Mod for 2007
- ↑ Honorable mention at the Mod DB Top Unreleased Mod for 2009
- ↑ http://www.moddb.com/events/2010-mod-of-the-year-awards/features/players-choice-upcoming-modification-2010
- ↑ http://www.moddb.com/events/2011-mod-of-the-year-awards/top100
- ↑ http://www.moddb.com/mods/operation-black-mesa/features/best-upcoming-mod-of-2013-players-choice
- Official website (Studio website)