The sound in that movie is great. The Zulu running. The Zulu chanting. The Zulu pounding on their shields.
The scene where the British form three ranks and then volley fire by rank is really good. You never see the Zulu falling. Then, the camera pulls back to show a huge pile of dead Zulu reaching ALMOST to the first rank. Really well done. Just quiet and shock on the faces of the British Soldiers.
Oh, how I love this movie! Your description alone raised the hair on my arms - and I’m not overly hairy.
Let’s not forget the subplot with a loopy Jack Hawkins who has to be locked in - I think - a wc for demoralizing the troops.