Space Forum / Space History / April 2004

It's more involved than that; historically, the different names go back
to the days of the old pre-Holland and early Lake boats- like Lake's
"Protector".
The submarine was designed to spend long times underwater, and tended to
be biased for that mission in it's hull design; the submersible was
basically designed as a surface vessel that could lower itself
underwater when the need arose (Lake's "Protector" was a submersible; it
was designed to roll along the seabed on wheels, rather than do much
maneuvering under power while submerged), and generally descended
underwater or surfaced on an even keel- after taking on or blowing
ballast- rather than angling itself downwards or upwards under power as
a submarine does.  The submersible's hull was biased for surface
operations in its hydrodynamic design, and it carried a large volume of
ballast tankage so that its reserve buoyancy put it quite high out of
the water when it was surfaced, but the vessel was only capable of slow
movements while submerged and tended to simply sink toward the bottom or
up rise from it, rather than engage in much underwater movement. The
submersible tended to use the sea to hide itself from the enemy just
before or after an attack, rather than as a means of stealthily stalking
its prey. The line between the two types got blurred fairly quickly,
(W.W. I and II subs tended to spend a lot of their time on the surface)
and nowadays a submersible is a small underwater vehicle that is
transported to it's destination by another vessel (either surface or
submarine) for it's operations. But their limited underwater endurance,
low underwater speed, and general movement in the vertical over
horizontal plane still harken back to the original meaning of the word.

Pat