The Collaborative International Dictionary of English v.0.48:
Submarine \Sub`ma*rine"\, n.
1. A submarine boat; a ship that can travel under the surface
of the water. Most such ships are ships of war, as part of
a navy, but submarines are also used for oceanic research.
Also called sub and (from the German U-Boot) U-boat.
esp., Nav., a submarine torpedo boat; -- called specif.
submergible submarine when capable of operating at
various depths and of traveling considerable distances
under water, and submersible submarine when capable of
being only partly submerged, i.e., so that the conning
tower, etc., is still above water. The latter type and
most of the former type are submerged as desired by
regulating the amount of water admitted to the ballast
tanks and sink on an even keel; some of the former type
effect submersion while under way by means of horizontal
rudders, in some cases also with admission of water to the
[Webster 1913 Suppl. +PJC]
2. A stowaway on a seagoing vessel. [Colloq.]
3. A submarine sandwich.