The Mary & John class Battle Destroyer was designed as a destroyer counterpart to the Heston class Battle cruiser and Federation class Dreadnought, utilising the same saucer design as those classes, with the upper nacelle mount from the Federation. Owing to wartime prioritising of existing designs, the USS Mary & John finally began trials in November 2257.
In common with the Twin Saladin and the Warhawk designs, the twin engine configuration was a reaction to the lessons of the four years war.
This class, however, fell victim to another lesson from the war Starfleet realised that a rationalisation of destroyer designs was required. Only the Warhawk class entered service, the USS Mary and John saw only limited service as the Heston/Federation class primary hull lacked the science facilities of the Constitution derived saucer of the Warhawk class, and as such was ill suited to the peacetime Starfleet.