These 28-gun sailing frigates of the sixth rate were designed in 1756 by Sir Thomas Slade "to the draught of the Tartar with such alterations withinboard as may be judged necessary". A total of twelve ships were built in oak during the Seven Years' War, all ordered from private shipyards; eleven of them were built over the relatively short period of three years; the twelfth was completed following the close of that war in a royal dockyard as its original contractor became bankrupt, and one further ship to this design was also built postwar in a royal dockyard.