So, lately, for a little while now, I have been thinking about this explanation theory that I personally have about the U.S. H.E.C.U. and Black Ops military and paramilitary forces in Half-Life (both the original game and Black Mesa, as well as their expansions). Most likely, accurately, and realistically speaking, these games probably don't just include U.S. Marine Corps troops alone, but also many U.S. Army troops and U.S. Navy troops, and maybe plenty of U.S. Air Force troops, as well as perhaps to sort of a lesser degree, plenty of U.S. National Guard troops as well, but probably not these last/latter two branches quite as much as the first/former three branches. (The Marines are primarily part of the U.S. Navy, but also overlap into the other two main military branches as well, and often or almost always work side-by-side as foot soldiers (also called infantrymen, commandos, or grunts) with the U.S. Army and the full-on main U.S. Navy, too.) There would also probably be both U.S. state (polity)-run paramilitary forces (including but not limited to, CIA and DIA paramilitary forces, such as the Special Activities Center (SAC), formerly known as the Special Activities Division (SAD), which includes the Special Operations Group (SOG), which includes black operations and many other activity roles). All of this could also probably be combined with some privately-run military and paramilitary forces as well, though this last part is not nearly as likely as everything else mentioned prior above. In fact, for example, the The Boeing AH-64 Apache attack helicopter is almost entirely used only by the U.S. Army alone and not the other three branches.