I keep on noticing this while playing Opposing Force and it’s getting really irratating: When you command an allied soldier, he may reply, “Sir, yes, sir.” This is innacurate. Adrian Shepard is a corporal, and should be addressed as “corporal,” not “sir,” as he is not an officer. Anyone else notice? Wait, allow me to rephrase, does anyone else care?
Nope
It was a good shot
But no, no one cares.
It’s not canon, and it’s not a real branch of the Navy either.
He wasn’t talking to you.
I know, the whole HECU isn’t a specific part of the military, etc. argument, but in the beginning, it specifically says Shep is a Marine, one would assume the guys he rode in with are also Marines. One would assume, since the guys that follow you are clones of the guys that ride in with you, that they are Marines. The Marines are not an imaginary branch of the US Navy.
But I agree, they should have just called them “Army” or “Marines” in HL1, instead of the whole damn HECU ambiguity thing.
Where are they called Marines? My brain’s a little foggy and I only remember them being called “soldiers”.
I think the PR value of going round killing hundreds of US Marines probably wasn’t worth it
I think you kill like 30 of them throughout the whole series.
Kevlar let me give you some advice. Never ask anyone if they care. By saying that you’re making it too easy to say, “no”.
They also refer to you as “Corporal” and “Marine”, which I guess is correct. If we really want to stick to realism, then we could assume the other soldiers around you make mistakes, calling you “sir” every once in a while. I mean they are dealing with aliens, it probably makes them forget about correct wording!
If anyone made that mistake I always used to hear the stock response, “Don’t call me sir, I work for a living”
He’s the highest in command in that squad at that moment, will have something to do with that
I dunno if this happens on other versions but here, in the spanish version they say ‘‘Yes, coporal’’ and ‘‘Yes, sir’’ They are using the two forms so I don’t care if a soldier calls me sir, after all Shepherd’s range is bigger than a range of a soldier…
At least the drill seargent in the boot camp training mentions something about marines if I remember correctly (I remember the sentence “god loves marines!” or something)
No.
The whole boot camp is awesome, because its a take off of the film Full Metal Jacket. So I suppose the references to marines are still there. Sounds to me like HECU is a part of the marines, hence the ‘U’ standing for ‘Unit’. If you’re in the SAS you’re still in the army, you’re just part of another unit
Regarding the whole ‘sir’ thing, the Royal Marines in the UK date back hundreds of years, and are full of little oddities that seem strange to others. I don’t see why the US Marines would be too different, maybe we could find one and ask 
It doesn’t say “Shep is still a Marine!” but it does say this:
He was trained as a Marine. It is entirely possible that he is on loan to another branch of the military, but chances are he isn’t.
This doesn’t specify who exactly the HECU are, only that they are there, and their CO on the Osprey has the same voice as the drill sergeant in the training level. It’s possible that the training level is basically just “this equipment is stuff that the HECU get and Marines normally don’t.” It never says when it’s supposed to take place, though, and it looks pretty much like everyone there is a raw recruit.
This actually makes sense in my opinion. All but one sentences I posted beforce (the wave sound file in my last post) are from the training, so maybe the boot camp training is some kind of flashback