Xyrillian ship
Xyrillian ships were utilized by the Xyrillians during the mid-22nd century.

Design
The ships had a tapering main hull with four nacelles, two on horizontal and two on the vertical trailing arms, with an apparent sensor array mounted between them.

These 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.

They were also 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" in a medium that wasn't water (as the Xyrillians weren't capable of producing it.)

History
In 2151, the  starship  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 Enterprises 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. ()

Background information 
The script for "Unexpected" describes the Xyrillian ship as "about half the length of one of [the] nacelles" from an NX-class starship. The Xyrillian craft was later referred to as "a small but exotic ship." This was the only use of the Xyrillian ship studio model.

As well as appearing in "Unexpected", the Xyrillian ship is additionally referenced in  and .

Starship classes