Fiend Without A Face (1958)

Arthur Crabtree directs this sci-fi horror about a long-range radar installation and its surrounding Canadian wilderness that becomes host to something deadly. At first, when military personnel and civilians are struck down, the leaders suspect murder, but the autopsies reveal that each victim has had their brain and spinal fluids sucked dry through a hole in the skull. Eventually the finger points to Professor Walgate (Kynaston Reeves) who has been experimenting with human thoughts, the results of which are invisible brain monsters.

When a massive dose of radiation then reveals the monsters, a gory showdown ensues.