Spear joined the Royal Navy during the American War of Independence and soon saw action at several of the largest fleet actions of the war. He was with Rodney's fleet at the relief of Gibraltar, fighting at the capture of the Caracas convoy, the Battle of Cape St. Vincent and then at the capture of a French warship and her convoy. His ship was again in action with a Dutch ship in the Channel, before Spear went out to the West Indies and saw action at the Battle of the Saintes. It was the start of an enduring connection with the Caribbean, where Spear spent the most active part of his career.