Redux of the Rusalka-Class Assault Frigate.
Top is production version (So far). Bottom is the one-off prototype.
She was originally a frigate competitor to the Ranger, but she did not outshine the Ranger's longevity on patrol. When the Antareans attacked, the design was revisited, revised, and pressed into service as an assault frigate.
Unlike the Ranger (which was constructed between several major shipyards as a symbol of unity in the ULP), the Rusalka was made from USN R&D- the research and Development arm of the Navy. Traditionally armed, part of the appeal of the Rusalka was originally the fact that it carried a balanced, conservative armament and could be pressed into service as a radar picket (which is why she has the nose-dome similar to the Loki and Fenrir, and the under-nose radar array). Obviously the admiralty favored the casual carrier and longstanding patrol nature of the Ranger, as a ship like the Rusalka didn't seem to have a future in what seemed to be the peaceful era at the time.