from Jackill's Star Fleet Reference Manual-Ships of the Fleet Volume I - by Eric Kristiansen

Notes:
        Touted as the Dreadnought of the Destroyer world, the Hellion Class of heavy destroyers has filled a void between Dreadnought and Frigate, giving policy makers the ability to extend mission specific military force to both boarder areas and home systems without provoking massive responses.
        When first launched, the Hellion was as powerful as a heavy Cruiser, making it a dangerous foe. The Mk I incorporated new improvements in warp engine design, shielding technology and computer control, as well as several interior components. Star Fleet R&D felt that a field test vehicle could increase the working knowledge of a multitude of systems without endangering the crew and ship. The Mk I’s compartmented design allowed entire sections of the ship to be removed or changed. This approach, usually only used on dreadnoughts, gives the Hellion surprising expandability and versatility. But unlike a Dreadnought, the Hellion carries no troops and a number of mounted systems that create a more stabilized platform, giving Fleet planners a unique cross between versatility and rigidity.
        The Mk I was the largest Destroyer Class of vessel for its day. Its powerful drive system gave the Hellion a unique forward attack profile, equal to frigates and heavy Cruisers of the day. The powerful FH-13’s gave the Hellion a first strike capability strong enough to fend off enemy Cruisers. Utilizing internal compartmentalization, the Hellion was able to take damage that would cripple other ships. The Mk I continued to serve as a primary combat vessel for two years until 2274, when the Mk II was introduced. The Mk II utilized the newly improved FH-9 phasers, giving the destroyer even more punch. With an increase in the shielding system as well, the Hellion continued to lead the pack of combat destroyers. The Mk III, introduced 14 years later, would be only a minor upgrage, increasing the primary computer core’s power, allowing for the introduction of the FSS shield system.
        But the Hellion was not immune to damage. Shortly after the Romulans began a massive aggressive push into the Triangle and Federation space, the USS Formathia and here escorting Baker destroyer USS Kimberly, engaged a Romulan type A Warbird that had crossed into Federation territory. In a vicious back and fourth battle, the Formanthia and Kimberly were both destroyed. The Warbird was later tracked to where is also exploded before crossing back into Romulan space. After studying the log of the Formatia, it was felt that adding an escort vessel to Destroyer Groups operating near the Romulan boarder, would allow the Federation to counter the Romulan Warbird threat.
        The Hellion was produced at the Smith & Smythe Construction Yard 2, Vannis and Argelius Fleet Construction Center at a rate of about 2 per year. The Hellion was the first vessel to have more hulls constructed than contracted for. Of the 26 constructed so far, 1 Mk III has been destroyed.