Molloy was promoted to post-captain on 11 April 1778, and given command of the 64-gun , flying the broad pennant of Commodore John Elliot. "Trident" sailed for North America on 16 April, and Molloy was present with Lord Howe's force at Sandy Hook on 22 July 1778, where the comte d'Estaing was successfully repulsed without an action being fought. Molloy was present at Howe's next encounter with the comte d'Estaing, during the Battle of Rhode Island in August that year, and on Elliot's return to Britain in December, Molloy took "Trident" to join Vice-Admiral John Byron's forces in the West Indies. "Trident" was part of Byron's fleet at the Battle of Grenada on 6 July 1779 and then at the Battle of Martinique on 17 April 1780. Molloy followed this up with service in the two actions off St Lucia on 15 and 19 May 1780, before handing over "Trident" to Captain John Thomas.