
The Diving Bell was a bathysphere, a deep sea exploration module, that could be winched down on a cable to the depths of the ocean. The Diving Bell was the property of the Nelson Institute of Marine Research (N.I.M.R.) which was marked around the entrance hatch frame and had the lettering "NIMR" along its circumference. As in the case of the second season episode Jonah and the Whale, it could be used as a rescue vessel.
In the script for Jonah and the Whale, Morton calls the diving bell "Seaview calling bell ... Urgent, repeat, urgent.", yet on screen he says "Seaview calling Apple One". Here the diving bell is clearly being referred to with the call sign "Apple One". The Apple One call sign is used again as the whale approaches the Diving Bell.
In the script for the second season episode The Deadliest Game, Nelson and Crane both use the call sign "Apple One" (see above). This is the only script we have found mention of "Apple One" so far. If anyone has other scripts referencing "Apple One", please let us know.
In the script for the third season episode Night of Terror, Crane simply calls with "Seaview to Diving Bell." Same in the aired episode.
The above is a photo taken behind the scenes during filming of the Voyage to the Bottom of the Sea episode "Escape" (later called "Deadly Creature Below") with Dawson Palmer and model Astrid Shultz playing around the full size Diving Bell.
Original Voyage to the Bottom of the Sea 7 Inch Diving Bell Miniature