This is a western only in the widest sense of the word, since it's not set in the Old West. It's set in the mid 18th century during the French and Indian War, on what was the frontier then. It can be seen as an adventure movie, although mostly it's a war film. It's also a character study of Major Robert Rogers, very well interpreted by Spencer Tracy, commander of Rogers' Rangers, an American military company of rangers attached to the British Army (this was of course before the War of independence).
The movie is harsh in its military objective (destroying an hostile Indian village) as in its depiction of the epic journey to get there and to get back. And its mostly about the journey, where Rogers pushes his men on a grueling trip through the wilderness, on boats and on foot, through sheer grit and strength of character.
Some reviewers have complained of "too much walking in the woods", but that's the point of the movie, showing how these men pushed themselves through such a harsh journey.
It's filmed in technicolor, and that's a good thing, because this movie needs a good cinematography. The cinematography we get is not perhaps breathtaking, but it's good enough to do the trick and get us into the story.
One complaint I have is that the actors, while dirty and disheveled through all the hardships, never really look like they are starving. Also, the actual battle, while not the climax of the movie, was not done that well, at least if we judge it by modern standards. But it doesn't really matter, because as I said what matters here is the journey and the determination to survive, and that is well depicted.
An intense, harsh, war movie made in 1940 for a nation that was about to get into the biggest war.
Curiously, despite the title, it has nothing to do with searching for the Northern Passage. That was supposed to come in the second part that was never filmed. In fact, in the credits it's called chapter I.
