Orca
The Orca is a Tau orbital dropship. It is entirely built for transport, and meant to operate outside of combat zones; it has almost twice the cargo capacity of the comparably-sized Thunderhawk, while only mounting an underslung turret for last-resort self-defense or clearing a landing zone. Imperial Armour Volume Three mentioned "unconfirmed reports" of more heavily-armed variants, though no models or rules for these have appeared yet (though now that flyers are king in 6th edition, that may change some day).
The Orca debuted in the Fire Warrior videogame, and Forge World gave it a physical model and rules in Imperial Armour Volume Three.
Battlefleet Gothic
Games Workshop must have run out of fish names, because they gave the Tau an escort gunship called the "Orca" as well. They are too small and too packed with weapons to mount a proper gravitic drive, so they get towed along in the FTL "bubble" of larger capital ships.