submarine (adj.)

also sub-marine, "situated, acting, or living under the sea," 1640s, from sub- "under, beneath" + marine (adj.).

"vessel that can remain underwater and be propelled when entirely submerged," 1899, short for earlier submarine boat (1640s, as a possibility), submarine vessel (1732), from submarine (adj.). Earlier as a noun it meant "a creature living under the sea" (1703, of coral).

The short form sub is attested from 1917. Submarine sandwich is attested by 1931 as an Italian-American food, presumably so called from the shape of the roll. Related: Submariner.