Early submarines as submersible torpedo boats

What did the early term submersible torpedo boat mean in practice?

Early submarines spent most of their time on the surface and submerged mainly for combat or concealment.

Early submarines spent most of their time on the surface. They submerged chiefly for action or to hide, including preparing an ambush. The term submersible torpedo boat reflects that pattern of operation. Their normal use differed from the modern expectation that a submarine remains underwater.