This is one of the most realistic war movies I've ever seen, and it's made more realistic by being filmed in an actual Southeast Asian jungle, presumably in Malaya.
It shows a late phase of what the Brits call the Malayan Emergency, 1948-1960. It was their Vietnam War, except they won. When I was a US soldier in the Vietnam War, we used to talk about this history.
If anybody asked how the Brits won it, I used to say, "Because Malaya is a long narrow peninsula surrounded by the sea and not bordering on China, and also because almost all the enemy fighters were Chinese, not Malays, easily distinguishable from the native Malays."
If you want to know what the jungles of Vietnam really looked and sounded like, watch this movie.