Romulan Clan-Ship

In the decades leading up to the Romulan Civil War of 2276, the descendants of the former Romulan Ship-Clans secretly built a number of enormous starships, intended as a refuge for Romulans fleeing the rule of the Star Empire. They later played an essential role in winning the war. 

Each ship was named after the Clan that built and operated it: the Tyrava, the Kaveth and one other of unknown name.

History
The ships were built secretly over many years, in response to increasing oppression by the Imperial government during the 23rd century. Exactly when the ships launched is unknown; for some time they operated secretly, their existence known only to a select group of Romulans loyal to the rebel cause. In 2276, when civil war became inevitable, the populations of all three ships took the decision to join the fight. In the event, only Tyrava and later Kaveth ever saw combat; the strength of support for the revolution meant that the third ship was never needed.

Arrangement and layout
The ships varied in design and layout; both of those seen by USS Enterprise consisted of multiple cylindrical hulls connected together, but in different arrangements. The ships were designed primarily as habitations, and their population included entire families with young children. Parts of the ships were laid out more like cities than ships, with large public spaces. The crew often used transporters to get from one end of the ship to the other. Both James T. Kirk and Ael t'Rlallieu remarked on the extravagantly large spaces inside the ships; this may have been psychologically necessary in ships designed to be inhabited for such long periods. Kirk estimated that the battle bridge of Tyrava was as large as one of Enterprise's recreation rooms, Ael that ChR Bloodwing could have fitted inside it (presumably an exaggeration).

The main transporter room on Tyrava was several hundred metres across and 40 high; this was a single transporter unit, large enough to transport an entire normal-sized starship. Spock explained that there were "certain economies of scale" for a ship able to afford enough power for such a strategy.

Tyrava, and presumably the others also, had no visible warp nacelles. Montgomery Scott's best theory was that the warp conduits might run down the centre of each hull, but he said that the population would have to be "suicidal maniacs" to try such an arrangement, unless they were far more certain than contemporary Federation shipbuilders could be that the warp system would never fail.

Tactical systems
The ships' main weapon was phased disruptor beams (which appeared blue-white). These probably used the hexicyclic waveform the Free Rihannsu had implemented on many of their weapons and shields, which gave them an advantage against opponents whose shields or weapons were not configured for them. The beams packed immense power, corresponding with the ship's size. During the Battle of Artaleirh, the first burst of fire from Tyrava destroyed five heavy cruisers within seconds (though some may already have been damaged). It took 34 Imperial capital ships to prove a match for Tyrava at the Battle of Augo. The Clan-Ships were, however, less agile than normal Romulan cruisers, due to their great size.

Tyrava was also described as carrying "a swarm" of smaller, armed craft; these could potentially have been fair-sized vessels themselves, since Veilt tr'Tyrava claimed to have holds capable of taking in ChR Bloodwing or USS Enterprise. All the Clan-Ships also carried large-class people-mover shuttles, for use if they found a world where they could start their own colony.