Llaiir'Dhael class

The Llaiir'Dhael class (Firehawk; FHA) was a type of warbird that was designed and built in the late 23rd century to counter the Federation Excelsior class. It was the heavy cruiser version of the Sparrowhawk light cruiser. Although this ship could be constructed with different modules, any given ship carried a single module type throughout its entire lifespan. (TOS video game: Starfleet Command I)

History and Variants
The Llaiir'Dhael class had several sub-variants throughout its life. It was used well into the 24th century, and it even served in the Dominion War, despite the age of the design. Some of these ships were powered by an artificial quantum singularity; other ships of any of the Llaiir'Dhael sub-classes had more traditional warp cores and four warp nacelles. 

Firehawk-K variant
A FHA could be refitted with K-modules, producing a FHK. This was an extensive refit, however. (TOS video game: Starfleet Command I) K-modules added disruptor firepower to the ship, even though no plasma tubes were added.

Novahawk
The Novahawk was the Heavy Command cruiser of the Firehawk series. It only carried K-modules. (TOS video game: Starfleet Command I)

Regalhawk
This ship was another Romulan effort to deploy more Type-R torpedoes. A variant of the Firehawk, it was less expensive and slightly less capable than the Royalhawk. These ships rarely operated alone, not from doctrine, but because their heavy torpedoes were in high demand for the most important ttacks. (TOS video game: Starfleet Command I)

Royalhawk
The RHK was a limited-production variant of the Novahawk. It was designed to field the massive Type-R plasma torpedo in greater numbers to counter the Gorn Strike cruiser. Like the Novahawk and its more modern cousins, it only carried K-modules. This ship could be considered a Heavy Battle cruiser back in its day. (TOS video game: Starfleet Command I)

Killerhawk
The ultimate expansion of the Heavy Hawk designs, this was essentially an attempt to build a pocket Dreadnought. This design was not considered successful since it placed too many weapons on too small of a hull. The maintenance cost to support this ship was far higher than any other Firehawk design. Only a few were built. (TOS video game: Starfleet Command I)

Known ships

 * Royalhawk subclass
 * IRW (destroyed in 2374)