The Federation Class Dreadnought was initially conceived prior to the Four Years as a variant of the Heston class Battle Cruiser (which was itself a Military role variant of the Constitution). The design was shelved as the new dilithium energised engines were not yet available to power such a large vessel. After the war the design was modified to take account of the lessons of the War and put into production using the new FWF-1 engine. The class was refitted in 2274, and was the most powerful Starfleet vessel until the introduction of the Excelsior class some twenty years later.