UNSC Atlantis (RelentlessRecusant)

The UNSC Atlantis is a deep-sea submersible originally designed by the UNSC Navy and later operated by the UNSC Special Operations Command and the UNSC Office of Naval Intelligence.

It is a small, self-contained deep-sea submersible capable of withstanding pressures in the gPa (giga pascal) range, tens of thousands of times higher than Earth's atmospheric pressure, and the Atlantis is believed to be able to dive to a depth of sixteen thousand feet, below the deepest trench in Earth's oceans (the Mariana Trench), but well within range of the trenches of other planets. The UNSC Navy originally designed the Atlantis for manned exploration of oceanic depths for research purposes; later the UNSC Medical Corps and Acumen Science Technologies would be highly interested in collecting biological samples from the lowest pits of the UNSC's oceans in the hopes of exploiting novel and previously unseen biological species for bioactive compounds (pharmacognosy).

However, by the time of the Battle of Earth, the Atlantis was repurposed. When Covenant maritime forces attacked the Yucatán Peninsula, searching underwater, SPARTAN-II Blue Team was deployed in the Atlantis to fend off the exploratory excavation. The Atlantis would be repurposed numerous times during the bloody struggle as the overwhelmed UNSC resistance attempted to aggressively attack underwater Covenant operations across the entire planetary theater of operations, and as the battle turned ill, it was proposed that the most senior UNSC command officers should be taken underwater in the Atlantis to remotely coordinate UNSC operations as the planet fell around them. The UNSC Atlantis never filled this purpose as the arrival of SPARTAN-117 and later, the Rtas 'Vadum's battle fleet would make that notion unnecessary.

Afterwards, however, the UNSC Atlantis dropped out from the mainstream, and was declared unusable for further academic research studies. Many have suggested that it is now in the possession of the UNSC Office of Naval Intelligence.