These vessels were partly organic in nature and the atmosphere was recycled by grass growing on the floor of the ships. They also contained tanks which stored "aquatic lifeforms." The vessels were equipped with advanced stealth technology and holotechnology. The latter was based on resequenced photons capable of projecting realistic scenery but not interactive characters, although far in advance of Human science of the time.
In 2151, the NX-class starship Enterprise discovered a Xyrillian ship hiding within the warp field of the Enterprise. Restricting the flow of the plasma exhausts, the Xyrillian craft caused various power drops and surges on Enterprise. Using stealth technology, the Xyrillian crew were seeking to use Enterprise's plasma wake to power their engines, their plasma coils having failed.
Upon the discovery of the Xyrillian ship, Commander Charles "Trip" Tucker offered his assistance but found the different atmosphere within the ship difficult to adjust to. Ah'len, a Xyrillian crew member, demonstrated to him their astounding holotechnology, and Trip was later able to repair the ship.
It seemed that Commander Tucker's repairs were short-lived, as the Xyrillian craft was thereafter found cloaked behind a Klingon ship. After the Xyrillians were discovered, the Klingons made a deal with the Xyrillian captain, as the Klingons were willing to let the Xyrillian ship go in return for implementing holographic technology on the Klingon ship. The deal went well and later the ship was repaired again by Commander Tucker. This particular ship had a complement of thirty-six Xyrillians and was commanded by a Captain Trena'L. (ENT: "Unexpected")