For passengers, as far as I know, only the "Night Ferry", between Victoria and
Paris actually did this, via Folkestone.

There was a freight-only equivalent via Harwich at one time.

The equipment used in both ports was a leftover from World War One equipment
installed to supply the troops!

There may have been others, but I am unaware of any.

The 1950s BTF film "Link Span" is a wonderful documentary showing just how this
operated.

Marc.