In the waning days of World War II, a group of Allied soldiers and reporters find themselves floating in a lifeboat, having survived the torpedoing of the troop transport on which they were previously traveling.  A mix of Australians, Brits, Russians, and Americans, the survivors are on the verge of giving up when they spot an apparently abandoned German boat floating in the middle of the ocean.

The survivors board the boat and discover that the crew is missing or dead.  The only survivor on the boat is a little girl (Ruby Isobel Hall) who hungrily eyes any open cut.  The survivors discover that the boat was supposed to be shipping art that had been stolen by the Nazis but that the boat instead picked up some unexpected passengers who wiped out the crew and who are still hungry for blood.  While one weaselly survivor resorts to trying to contact the Germans for help, the others try to stay alive in an environment that they can’t control.

Blood Vessel owes an obvious debt to the Alien franchise, with the survivors roughly corresponding to the space marines who failed to stop the Xenomorphs in Aliens and the ship acting as a water-bound version of the rickety spaceships that have appeared throughout all of the Alien films.  There’s no real surprise to the nature of the monsters that have taken over the boat.  The film’s entire premise is right there in the title.  But Blood Vessel is claustrophobic and the monsters, when they do make their eventual appearance, are frightening in both their ruthless savagery and the mocking joy that they take in their activities.

All the more memorable for having been shot on an actual boat, Blood Vessel is effective low-budget horror.