During the Empires period - especially the Conver War - the Solar Dominion often found itself needing to consolidate its hold on newly captured systems, as well as in need of a propaganda tool that would help sway the allegiance of neutral worlds. The result - the Empire Ship
Basically a combination of Corporate Ship, System Control Battleship, Linelayer, sub-ISO, and Temple Ship, the Empire Ship announced to those worlds that had never heard of the Dominion, the God Emperor or the Lord of Rays, or had only passing knowledge, the glories of the empire, and provided an invitation to join. As the Empire Ship was far bigger than anything the locals had ever seen (the exceptions were those old-timers and relativists who remembered the days of the Federation Company Ships, but these were few)
The Empire Ship - several kilometers long at its long axis and massing many tens of millions of tonnes - would serve as a capital ship (in case the nearby hostile polities or fleets), orbital culture platform, memetic base, factory, gift-shop, embassy, and more. They provided the locals with gifts (mostly luxury items of no strategic value), artwork, and other consumables, and conduct guided tours for visitors. The locals would be shown around huge biospheres filled with all sorts of marvellous plants and tropical birds, the mighty Diametric Drive engines, the awesome weapons platforms, the magnificent Temple Rooms, the sumptuous Lifestyle Modules. Although the crew of the Empire Ships would never attempt to convert anyone (at least not in a way that a <S1 sapient could tell), gradually these magnificent vessels inevitably would make an impression, along with all the gifts they provided (hence the popular alternative name - Cornucopia Ships), and their crew would help with local development projects and building up of infrastructure. After a few decades the system would be pretty well memed, the wormhole would be established (although it might take another century for it to be inflated to full size) and the empire ship would move on to the next port of call.
In subsequent centuries the Empire Ship became enshrined in Dominion culture, their calling card to other polities. Of course not every system or polity was or is lucky enough to get a visit from an empire ship. Empire Ships are big, expensive to run and maintain, and are generally only sent to favoured or strategically important polities. Lesser important polities may get a visit from a smaller ship like a corvette, or perhaps a linelayer corps of engineers might establish a stargate in their system, if they are strategically or economically important enough to qualify.
The development of the Triumvirate Civilization Ship (or CPNC Ship) was quite a blow for the Dominion. For centuries their Empire Ships were the most magnificent vessels of the space lanes. Although mobile ISOs, worldships, and some MPA megaships were often in part much bigger, these were always one-off affairs, interesting for a while, certainly, but then moving off to undertake some obscure agenda of their own. But the magnificent Empire Ships were always there, unmatched in their splendour as the greatest single design-type.
With the launch of the Evergreen Future - the first CPNC Ship - in 7561, the fad-hungry sentients of the galaxy suddenly lost interest in the Empire Ships. The Dominion responded by building even bigger, more expensive, and more sumptuous Empire Ships, although this could also be seen as an ongoing trend towards greater magnificence and ostentatiousness, especially in the optimistic post Paradigm containment war era. The H. H. Daniel Borde (the 15th vessel to bear that name) for example was an enormous 53 km in length, the Fons Luminis 68 km, the Shamesh at 81 km, and finally the Amen Ra 112 km in length, the largest and most expensive vessel ever constructed by the Dominion. But not only did these vessels not match the Civilization Ships in size, but - despite some notable successes, such as the conversion of the entire Wu B-Som Combine to the Dominion following the extended visit by the Fons Luminis in 7864-65 - their ostentatious memetic was still hardly comparable to the grand selfless purpose of the CPNC ship, and their success rate among undecided polities was only a little better than that of standard empire ships. In any case the 7812 economic recession in the wake of the Qugaun scandal meant the Dominion was forced to cut back on its grand scale ship building, and no more Empire Ships were launched for another fifty years. The next Empire Ship, the Rays of Glory, was a "mere" 6 km long.
In times since, the fates of the Empire Ships have been various. In the early 8000s the most gigantc empire ships, being far too expensive to maintain, were converted into orbital habitats and temple complexes, where they remain happily to this present day. From that time on no Empire Ships have exceeded 30 km in length, and many are less than half of that length. At least five Empire Ships have been captured by the Amalgamation in the last few centuries, much to the discomfort of the Dominion. Currently the Dominion fields some 51 Empire Ships, the largest, the Pride of Aton, being 29.2 km in length. The oldest currently active Empire Ship, the 8 km long Great Helios (upgraded from its original 3.8 km), was commissioned during the middle Consolidation period. These beautiful vessels continue to ply the space ways of the middle regions and the outer volumes, and the arrival of an Empire Ship is always an event of great excitement and importance. Many polities have national holidays based on the arrival of an Empire Ship centuries or even millennia ago. A number of decommissioned empire ships have been give their freedom and each has been awarded The Crest of Honor for Long Service to the Empire by the God Emperor Himself. These vessels make a living touring the galaxy and entertaining sentients with tales of their adventures and life as an empire ship.