UFO: Sub Smash (Episode 8)

After an underwater UFO has attacked and sunk a freight ship in the ocean, Straker, Foster and SHADO lieutenant Nina Barry join a submarine crew to find out what they can. However, they too are attacked by the UFO's vessel and, as a result, their submarine is grounded on a ledge. Straker has to overcome his claustrophobia in order to work out an escape plan.