Conway was the British military second in command on the Rochefort expedition in 1757, and repeatedly advocated an attack on Fort Fouras, but his colleagues would only agree a night attack (which failed). Ultimately the expedition returned to Portsmouth having achieved nothing. Though Mordaunt (the commander in chief) was acquitted by his court-martial, the affair damaged both their reputations. In his displeasure, George II refused to employ Conway on the 1758 campaigns. He was not employed again until the next reign, except that he was sent to sign a cartel for an exchange of prisoners at Sluys in 1759. On 21 April 1759 he became colonel of the 1st The Royal Dragoons and on 25 August 1759 he was promoted to lieutenant general.