A previously unseen type of UFO is seen operating underwater at the beginning of the episode. It soon destroys a freighter sailing on the surface.

The life preserver floating in the sea after the destruction of the freighter at 2:05 on the DVD identifies the ship as the Atlantica from Penarth, Wales, United Kingdom.

This episode reveals that Straker suffers from claustrophobia.

This episode reveals that Skydiver has the capability of "seaskimming", i.e. travelling rapidly over the ocean surface.

At 9:15 on the DVD, actor Ed Bishop's blue television eyeliner make-up is quite obvious!

The rescue plane that searches for the crippled Skydiver is SHADAIR Albatross 15. It will also appear in "Reflections on the Water".

At 29:50 on the DVD, the air regulator on Lt. Lewis' scuba tank is a Mistral. This is a brand made by Aqua Lung.

Just before the rescue of Straker and Lt. Barry is affected, we hear Straker's thoughts, as he believes they are going to die in the sub; they are a variation on the Burial at Sea prayer often used by sailors to commit the dead to the sea.

After visiting time is over with Straker and Nina, Freeman says, "Well, back to the salt mines." This is an idiom which basically means it's time to return to work, with reluctance. The idiom originated with Russian prisoners in Siberia, who were forced to work the salt mines there in the 1800s.

There is the hint of an attraction between Lt. Nina Barry and Commander Straker in this episode, but nothing is seen to come of it throughout the series. 

NOTES FROM THE AUDIO COMMENTARY BY ED BISHOP ON THE DVD

Bishop (Commander Straker) notes the scar visible on his lip at about 22:20 on the DVD. He says he received the scar when he was in the Army.

Bishop tells that the watch worn by Straker throughout the series was given to him at the end of the season shoot and he continues to wear it to that day. (Bishop died in 2005.)

MEMORABLE DIALOG

a morbid dread of confined spaces.wav

cat and mouse.wav

I'm glad it's you.wav

the things we never say.wav