Black and white war movie where squad is under fire in water at the end.

My mom was busy housecleaning and let me stay up too late one Friday night watching TV when I was six, so roughly Jan/Feb of 1970. The movie was a black and white war movie, probably WWII or Korea vintage. Movies weren’t being made about Vietnam yet, and that war was still going. I’m guessing the movie was quite a bit older, probably from the late forties or into the fifties, as first run or recent movies didn’t exactly show up on local TV on a Friday night. I remember the movie as being grey and green, but that might have been the quality of our TV, or it could have been shot with a filter. No night imaging yet at that time and not as bright green as infrared night vision. I thought it was a John Wayne movie at the time, but I’ve been through his catalog and haven’t found it. Commanding officer in the movie resembled him, as I remember. It was definitely an American movie, accents were American. I mainly remember the platoon in the movie trying to build some sort of a structure like a dock or bunker, some sort of wall in water out of wood or bamboo poles, and being strafed from the air by enemy planes at the end. You could see the water jumping as bullets hit it. I’m guessing it was Pacific theater WWII. They were wearing helmets with the netting over it, like American soldiers. I can’t even remember a historical event that the movie could have been based upon, that matches my memory of the movie.