I used to watch it (or something very similar) being tested here in our 'secret location'. It went through a great deal of development, with new bits added every time it appeared. All a bit James Bond.
'Tomorrows World' came all the way from their comfort zone to film it for the programme. Sadly the weather was terrible - gale force winds and heavy dark overcast. The underwater camera crew were really cheesed. 'How do you expect me to film a black submarine in the dark?' I think they did get some shots of it on the surface though.
Handy for me though, they chartered my ketch for three days to do a sequence on a talking echo sounder - I kid you not - designed to help the single handed sailor. We had great fun trying to hide ten people down below while the 'starlet', apparently sailing alone, sipped his gin in the saloon while listening to the sexy electronic voice calling the depth. We were sailing directly towards another film crew marooned on an island, with me steering with one finger while hiding in the companionway and looking astern
. When they radioed they had a great shot the starlet emerged and tacked the boat - sh*t, we were really close
. The echo sounder didn't scream, just told us the water was getting deeper. All in gale force winds.
There's more to the tale, but it could be boring.