The Atomic Submarine

The Atomic Submarine is a 1959 independently made American blackandwhite science fiction film produced by Alex Gordon, directed by Spencer Gordon Bennet, and starring Arthur Franz, Dick Foran, Brett Halsey and Joi Lansing, with John Hillard as the voice of the alien. The film was distributed by Allied Artists Pictures Corporation.

Commander Wendover orders the submarines most powerful torpedoes fired. They reach the saucer but do not explode, being stopped by a gellike extrusion coming from within the UFO. The captain knows that he must stop the ship sinkings, so he orders Tigershark to ram the alien saucer. The submarines bow tip breaks through its lower side and becomes trapped.Dr. Neilson pilots Lungfish, taking Lt. Commander Holloway and a small party to board the UFO. While Dr. Neilson waits on the minisub, Holloway has the boarding party cut free the bow with blowtorches. Meanwhile, he explores the saucers dark hallways and receives his first telepathic message from its sole occupant, an octopuslike creature with a single large eye for a head. The alien proves its hostile intent by remotely killing all the boarding party except Holloway. The creature announces that it plans on bringing several human specimens back to its home planet for further study. The aliens plan is to modify themselves, based on what they learn about humans, and once finished, they will come back and take over the Earth. ........

Source: Wikipedia