The Tunnel

people often assume there is symbolism in films when sometimes there isn't any.

dreams are not just symbolic content.

it could be a reference to the western notion of the 'dogs of war', which is a reference to
a line of shakespeare that is about the brutal and savage, unfettered destructiveness of war.

however, you have to put the dog in context.....the dog appears in front of the tunnel, barking and baring teeth, and growling. It seems like it is associated with the tunnel, and that it might attack.
It also comes out of the tunnel.

So I think it is like Cerebrus, the Greek gatekeeper of the Underworld...the tunnel is the underworld where the dead exist.

And in psychological terms would be the unconscious. The captain, or sargeant is overcoming
his being haunted by the ghosts of the men who died under his command.

the dog appears on the other end of the tunnel, again as the gatekeeper, i believe.

That's not "Black Orpheus". That's just Orpheus. The film "Black Orpheus" is a modern retelling of the Greek myth of Orpheus. In the Orpheus legend, in which Orpheus descends to the underworld to rescue his lover from death, the underworld is guarded by the dog Cerberus. "Black Orpheus" tries to present, with mixed results, a realistic depiction of the Orpheus myth in which the underworld takes the form of the Carnival in Rio. So it would make much more sense to mention Cocteau's "Orpheus", the original cinematic adaptation of the myth, as a reference, rather than "Black Orpheus" (unless Cocteau's adaptation omitted the dog -- did it? I don't remember.)

First Chapter Name:
The snarling sentinal

Last Chaptr NAme:
The sentinal returns

I believe that the dog is a guardian of the tunnel which is a zone in which the dead wander. By misguarding the dog and passing through the tunnel, the commander awakens his fallen comrades. At the end, the dog seems more angry and aggressive and "tells" the commander to move away, to let the fallen rest in peace.

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It is also believed by some that animals can sense the dead. So perhaps this helps to explain the appearance of the dog a little more.

That also confused me. It helped that a friend pointed out that the things the dog seemed to be carrying looked like gernades that the Japanese made during WWII. Possibly, it is simply a reminder of the pain that the commander has been through. First losing his battalion, then being locked up in a camp (with dogs guarding, I'm sure), and then the long battle with himself. If anything, the dog is a guard, much like the function would be in real life, and is simply a reminder to the commander what he's been through, and what he has done in the past. Much like an emotional scar for soldiers.

I also liked the film. I actually just got out of seeing it (we had to watch it for a school assingment and the teacher showed it to us in the auditorium movie-theatre style), and I was hoping to find more information to make some scenes make sense.

I buy your interpretation, Vikingou, but I'm not sure it matters. There CAN be more than one way to understand this movie. The beauty about this movie is that you take from it what you will.
My interpretation - most of the sequences ended without the action being resolved. The man is being chased by a demon and the scene ends, the boy travels under the rainbow and the scene ends. With that in mind, I interpreted the dog as the personification of War, and, although small in size, he seemed more than a match for the commander. Either the commander escaped after the scene ended, or he was defeated by the dog.