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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 11 ft (3.4 m)) version of the Valiant class, the lines of which were taken from the French Invincible, captured in 1747.