The Ajax-class ships of the line were a class of two 74-gun third rates of the Royal Navy. They were grouped in with the large class of 74s, as they carried 24-pounders on their upper gun decks, rather than the 18-pounders of the middling and common class 74s. The design of the Ajax class was a lengthened (by ) version of the , the lines of which were taken from the French , captured in 1747.