A Dhow is the sublight starship of the xenos Nicassar species, one of the member races of the T'au Empire. Dhow are relatively small star-faring yachts, propelled primarily by their Nicassar captain's potent telekinetic powers, abilities which often determine who rises to positions of leadership in Nicassar society.
Nicassar starships are primarily sleeper ships, in which the majority of the crew enter a state of hibernation that the Nicassar's alien physiology makes possible as the flotilla, consisting of multiple Dhows docked together, drifts between the stars, directed by the efforts of a few non-hibernating Nicassar crewmen.
Although poorly armed when they first encountered the T'au, the original weapons employed by Nicassar Dhows have been upgraded with T'au Railgun batteries. The T'au Empire uses Nicassar Dhows as Escort vessels for the T'au Navy, towing them across interstellar distances using the limited "Warp Dives" employed by T'au starships to travel across the galaxy.
The Nicassar's extended families are semi-nomadic and are driven by a truly insatiable curiosity. This led to the original exploration of their home star system, as they are only truly content when travelling. Because they can survive for long periods in virtual hibernation as a result of their alien physiologies, they have travelled far from their homeworld, albeit slowly.
First contact between the Nicassar and the T'au Empire came when a T'au Gal'leath-class explorer vessel was setting up a waystation in interstellar space and sighted a Nicassar flotilla that had been in space for centuries.
As members of the T'au Empire the Nicassar must serve the Greater Good and do so by providing fleets of Dhows to scout and explore star systems on the fringes of the T'au Empire. They are transported to their station by T'au vessels using gravitic hooks that are capable of interstellar travel through the Warp and commence a leisurely circuit reporting anything they find.
When a Nicassar family travels, numerous Dhows travel docked together forming a larger community in which some members will be hibernating whilst others remain on watch.
- Battlefleet Gothic Armada - To Unite the Stars: Tau Vessels, pg. 107