Old takeover horror movie

This is something that bothered me for about 30 years. When I was about 10 I saw a couple scenes of this movie (might have been a tv show) which still haunt me. So the movie should be quite old, but it was in color. I watched a german version.

The only thing I remember is that there is a crew, possibly of a ship or submarine. It didnt seem SciFi. They are taken over/infected/assimilated by a monster/alien thing. There is a scene where one guy gets taken in what I think was some sort of locker room, not sure. I closed my eyes before I could see the monster. Afterwards a group of taken over crew discusses that an officer (maybe captain) struggled so much he almost died. So not a Thing situation where the audience doesn’t know who is taken over.

That is it. I watched maybe 5min but they keep inspiring nightmares. Any help is very much appreciated.

Might it be the 1989 film Leviathan? (The link is to a wiki article that gives a better, more detailed summary of the film than I could give.) The film drew heavily on Alien and The Thing. The setting is an undersea mining base. The crew discover and explore a sunken Russian ship and recover a safe from the ship, which contains a log, some video tapes, and a flask of vodka that two of the crew drink from. Unfortunately for them, the video reveals that the Russians were conducting some sort of experiment in genetic mutation that got out of hand and wiped out the entire crew. The vodka was tainted. The two crew members who drank the vodka begin showing signs of illness and mutation, and they eventually die. But their bodies mutate into a frightening looking monster which attacks and infects someone else, starting a cycle of infection and mutation among the crew of the mining base.

I don’t remember the film well enough to recall if the two scenes you described were in there, but I saw the film in the theater about 35 years ago, so it is old enough to be the film you are looking for, and it is a about an undersea crew being infected/assimilated by a monster. It had a decent director (George Cosmatos), a decent budget, a fine cast, and good special effects. I remember it got a lot of bad reviews when it was released, but I liked it. It might be the film you are looking for.

Thanks, but it is not leviathan. I think it might be older than that and at least the scenes I saw were an all male cast. Also the monster/alien in the movie does not primarily kill but take control of the humans. At least in the scene I remember.

DeepStar Six (1989)?

Maybe The Intruder Within (1981)?