The Ocean Troop Transport (OTT), alternatively known as the S-TRN, served as a submersible transport for the Trade Federation, facilitating the movement of B1-series battle droids both above and below the water's surface.
This vehicle was known for its sluggish maximum velocity and a tendency to submerge unexpectedly. It was more dependable when functioning as an aquatic surface repulsorcraft. There were two iterations of the vehicle: an armed version and an unarmed version. The armed version was classified as a battleship.
The OTT played a role in delivering battle droids to execute attacks on the settlements of Spinnaker and Theed. Potentially a derivation of the MTT, the OTT also saw action during the Battle of Naboo, where it was used to assault the submerged Gungan settlements.
Within Secrets of Naboo, these vehicles were simply called "submersible tanks." Star Wars: Galactic Battlegrounds employed the designation "S-TRN," which ostensibly stood for "Submersible TRaNsport." The New Essential Guide to Droids utilized the term "OTT," an acronym for "Ocean Troop Transport."
In response to an inquiry about the OTT, Leland Chee verified its equivalence to the S-TRN from Galactic Battlegrounds. Chee clarified that the OTT was a distinct vehicle from the MTT, not merely a modified version, despite their apparent visual resemblances.