“Sub-Smash” is episode eight of season one of UFO.
A ship, Atlantica 4, is attacked by an underwater craft. Skydiver 1 approaches the site of the attack on the surface and reports to SHADO Control that there are no survivors and some evidence of UFO.
At SHADO, Freeman and Straker discuss the attack. They think it was the UFO that slipped in a month ago, perhaps a special underwater craft. Straker is going to head out himself for a detailed search in Skydiver. Freeman asks Straker if Freeman shouldn’t go instead. It seems Straker has claustrophobia.
Skydiver is on the surface and Foster and Straker are discussing things. The theory is that UFOs are taking people from at sea. The sub’s captain orders a surface sweep, followed by an underwater one. Straker heads below and chats to the crew; he’s not entirely comfortable.
Lt. Barry reports a metallic object doing 60 knots underwater 2,000 yards away. The captain tells Foster to get below as they’re going down. Straker is informed. There’s nothing on the cameras, then sonar contact with the object is lost.
Then the UFO fires on Skydiver, injuring Chin. They fail to surface and a turbine blows. The UFO goes past them and heads to the surface. Sky 1 is sent after it, and destroys it. It has no contact with the sub, which heads to the sea floor. Sky 1 tells SHADO Control that Diver 1 is out of contact and there’s wreckage. It heads to base as a marker buoy surfaces.
Straker assigns everyone tasks, as the sub’s captain is now on Sky 1. Freeman is heading in on a rescue plan and they’ve got the beacon.
Diver 1 has 8 hours of air and power at most. There is hydrophone communications through the buoy, and that’s it, and only one escape hatch is functioning, and that not well. All this means the claustrophobic Straker is trapped in a tin can underwater.