Cloaker

While lightly armed, the cloak frigate has one asset that is perhaps far more valuable than any weapon: the ability to cloak itself and any nearby ships within a massive spherical field. Allied units within would appear to not be there, while environmental objects such as asteroids would still appear. While the field is large enough for all the ships in a fleet to huddle under a single cloak frigate's field, they would be incredibly compacted and less capable of fighting effectively if they did so.