Yup, back again... sorry for the tangent, your work obviously resonates with a few of us!

[USER=22208]@Phillip1[/USER]   Your build picts, the colours; the simplistic, tidy view of technology at that time...

Just couldn't shake some memory buried back in my brain...

subs... maybe, a perpetual 'ping'

mermaid?... vague

Thunderbirds?... weren't those flying?

puppets... spooky marionettes?

then I found it! 

1964, on TV!

Stingray!

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Following up on my first thoughts, also in 1964,

Voyage to the Bottom of the Sea

Ping... ping.... ping

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