UFO: Destruction (Episode 9)

Aliens attempt to destroy a naval ship dumping toxic waste into the ocean but their craft is shot down. Straker is surprised to read the news of the incident as it was not a SHADO operation, and goes to see Admiral Sheringham at the Admiralty. Sheringham is not co-operative and Straker suspects a cover-up. He sends Foster to see if he can get more information from Sarah, the Admiral's secretary.