The history of torpedoes is fun. The original ones were attached to a spar at the front of boats. The boat had a steam engine which they used to get up to speed to try to ambush and ram enemy capital ships. The threat these boats posed to capital ships gave rise to "torpoedo boat destroyers", which we just call "destroyers" today.

The first kinds of torpedo boats that launched stand-alone torpedoes did use torpedo tubes, but they weren't underwater. Underwater launching of torpedoes only started when torpedo boats evolved into U-boats (undersea boats, a.k.a. submarines). Destroyers remained torpedo boat destroyers, but now rather than hunting small, fast boats on the surface using small, fast guns, they hunted stealthy boats that were underwater with depth charges.