well, I think there's only one way to make a playable blimp. It's absolutely impossible to get a playable sub to fly, but if you put the 3d model let's say 300 m above the subs origin node the 3d model will 'fly' 300 m above the sea when at surface, and will skim the waves when at 300 m depth.
only problem is, you can't fly over land and you run out of oxygen when below 300m of altitude.
for 3d-editing you can use any program that supports the .obj file format, as that's the format S3D uses for importing and exporting.
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