The R'Keth class battlecruiser was first deployed during the "Dueling Birds War" between the Romulans and the Klingons in the 2130's. The Stormbird was so effective, the Klingons used it as the basis for their D-series battlecruiser designs over the next century, using plans and tech stolen by Klingon agents. Heavily armed and shielded, the Stormbird's biggest threat was its forward anti-proton cannon which was devastating to both space-based and planetary targets.
The D'remelak-class destroyer, code-named "Raptor" by Starfleet, was a lethal addition to the Romulan Imperial Navy. It was heavily shielded and carried a powerful forward disruptor cannon. The Raptor could also be fitted with a package of between four and six atomic weapons, each with a variable yield of up to ten kilotons. Because of its heavy armaments and armor the ship was slow in combat, making it vulnerable to coordinated attacks by Starfleet.
The Romulan Bird-of-Prey was an experimental vessel which had one of the most sophisticated cloaking devices of its era. The Bird-of-Prey was originally built for service to the Tal'Shiar, but when the Praetor declared war on the Coalition of Planets, the ship was commandeered by Valdore's navy to raid Earth convoys. The Bird-of-Prey's effectiveness was reduced greatly once Captain Archer was able to penetrate the vessel's cloaking device. After the war was over, the Tal'Shiar reclaimed the few ships of the class that survived.
The N'Kentha-class destroyer was a potent ship of the line which had proven itself during the Romulans' expansion into Klingon territory nearly two decades earlier. While the Warhawks were old, they were reliable, maneuverable, and easy to build (they constituted over a third of the fleet Valdore deployed against Earth). The Warhawk, like all Romulan warships, carried a self-destruct device which could be activated instantly by the Romulan commander.
When the first Romulan Warbird-class vessels were decimated by the Klingons in the 2130's, the Imperial Navy decommissioned them. Before the Warbirds were scrapped, Technology Czar Nijil and Admiral Valdore appropriated and refit several of them into a specialized configuration that allowed for experimental weapons testing. The newly-christened "Marauders" served as the testbed for a failed holography package against the allied powers in 2154. Nijil and Valdore retooled the last remaining Marauders to carry the highly effective r'renw'huae device which could remotely hijack an enemy ship's computer. It took Earth nearly three years to develop a countermeasure to the Marauder's telecapture device.
The Bochra-class carrier, known as "The Dragon" was the largest ship in the IRN and served as a base of operations after an enemy planet or base had been pacified. The Dragon carried a complement of Blackhawk attack fighters, support craft, and had a primary launch bay which was large enough to accommodate an entire starship in the event major repairs were needed. The Dragon could achieve a maximum speed of warp four and its standard crew complement was over 2200, with over half of those being Reman infantry.