In the Video Game, Half-life, what type of US military force starts clearing out the Black Mesa Research Facility?

The HECU (Hazardous Environment Combat Unit) is the type of US military force that starts clearing out the Black Mesa Research Facility in the video game Half-Life. The HECU is a specialized military unit trained to handle hazardous environments and combat situations, which makes them well-equipped to deal with the unusual and dangerous situations that arise in the facility. Their main objective is to contain, neutralize, and eradicate any threats present within the facility, including alien and mutant creatures.