"I just overheard a secure access transmission: soldiers have arrived and they're coming to rescue us!" ―Black Mesa Scientist The Hazardous Environment Combat Unit, often abbreviated as HECU, is a United States Marine Corps special forces unit featured prominently in Half-Life and its expansions. "I've killed twelve dumb ass scientists and not one of them fought back... This sucks." ―HECU Marine The soldiers of the HECU are specially trained to deal with a variety of indoor combat situations, particularly involving a dangerous environment and unconventional enemies. Members of HECU are trained by drill instructors Dwight T. Barnes and Sharpe, and train at bases guarded and staffed by members of the Military Police. The Marines are often referred to as "grunts" by fans of the game, and also as such by Black Ops operators in the game. They are featured in Half-Life, and its expansion packs, Opposing Force, Blue Shift, and Decay. "I didn't sign on for this shit. Monsters sure, but civilians? Who ordered this operation, anyway?" ―HECU Marine[src] Following the catastrophic Resonance Cascade at the Black Mesa Research Facility, bizarre aliens from Xen teleport into the complex and begin attacking personnel. The Hazardous Environment Combat Unit is dispatched to the facility to fight the aliens and regain control of Black Mesa. Unknown to the surviving personnel at Black Mesa, though, the Marines have also been ordered to eliminate Black Mesa's civilian personnel to ensure that the incident is covered up. The HECU rapidly takes over the surface areas of Black Mesa and dispatch forces into the interior to eliminate the aliens, Black Mesa Security Force, and bring important members of the Science Team up to the surface for brutal interrogation. Many soldiers disagreed with their orders. The HECU's initial foray into Black Mesa was highly successful. The Marines quickly gained an advantage over the confused and frightened survivors and aliens and established a substantial presence within the facility. Black Mesa's civilian personnel failed to put up any notable resistance, as many personnel mistakenly believed that the Marines were there to rescue them, and those who tried to defend the facility against the HECU were hopelessly outgunned and overwhelmingly outnumbered, having already been weakened by the Xen creatures. The HECU soon took control of Black Mesa's central command areas and issued orders over the public address system for the facility's remaining personnel to cooperate and submit to interrogation. The troops began fortifying key surface areas with sandbags, mounted machine guns, and fixed artillery. Although there were few of them, there were also some snipers, one of which shot at and fatally wounded a security guard. The tide soon turned against the HECU, though, as the Xen aliens continued teleporting into Black Mesa in overwhelming numbers. Surviving facility personnel lent their help to Dr. Gordon Freeman, who was able to sneak and fight his way across the facility despite all the HECU's defenses. Freeman quickly became a priority target of the troops. Their anger toward him was exemplified by several sets of graffiti seen in the "On A Rail" chapter of the game, which read "YORE DEAD FREEMAN" , "SURRENDER FREEMEN" , "DIE, FREEMEN" , the latter of which is accompanied by 1 or 2 tripmines. Also in the same chapter two Marines can be heard talking about Freeman and their proposed revenge for killing so many of their friends, ignoring the irony of what they themselves had been doing. The full conversation is as follows: * "So, who is this guy, Freeman?" * "They say he was at Ground Zero." * "Science Team? You think he was responsible, sabotage, maybe?" * "Yeah, maybe. But one thing for sure is he's been killing my buddies." * "Oh yeah, he'll pay. He will definitely pay." As the battle raged on, the Xen aliens began to gain the advantage and the HECU, which was sustaining appalling casualties, was evacuated as aerial bombardments tore into the facility. The evacuation was woefully incomplete, however, leaving many Marines behind in the facility (in blatant violation of the policy never to leave another Marine behind) in the unenviable position of being caught amongst the forces of the Black Ops, the Xen aliens, and the newly-arrived Race X creatures. Still, the HECU was aware of this happening to some degree, as a soldier was able to send one last radio transmission to any stragglers underground. "FORGET ABOUT FREEMAN! We are cutting our losses and pulling out! Anyone left down there now is on his own! Repeat, If you weren't already, you're in a..." more info goto http://half-life.wikia.com/wiki/Hazardous_Environment_Combat_Unit