Submarine

Submarine may refer to several vessels in the Grand Theft Auto series:
 * USS Numnutz - A prop submarine in Grand Theft Auto: San Andreas.
 * Kraken Submersible - a single-person submersible vessel in Grand Theft Auto V and Grand Theft Auto Online
 * Kraken Kraken - a single-person submersible vessel in Grand Theft Auto V and Grand Theft Auto Online
 * Ramius, Bogdan's vessel in the The Doomsday Heist update for Grand Theft Auto Online.
 * RUNE Kosatka, the player-owned command vessel in the The Cayo Perico Heist update for Grand Theft Auto Online.
 * Kraken Avisa - a four-person submersible available as an upgrade with the Kosatka in GTA Online

It could also refer to vehicles that can convert to submarine vessels:
 * Stromberg
 * Toreador

You may also be looking for the following underwater missions:
 * Submarine Pieces - Collectibles in GTA V
 * Setup: Submarine Recon - A Doomsday Heist setup mission in GTA Online
 * The Merryweather Heist - A Heist in GTA V featuring the Submersible.