At about 08:30 on the morning of 20 June, "Yankee" sighted a steamer lying in Casilda harbor closely fitting the description of "Purissima Concepcion". The American ship stood in as close to the shoals as she dared and then fired a shot across the steamer's bow in an unsuccessful effort to make her show her colors. Instead, the merchantman began preparations for getting underway. Yankee responded by opening a steady fire at extreme range. As the supposed Spanish steamer moved farther into shoal water and disappeared behind some islets, "Yankee" shifted fire to an enemy gunboat and a floating battery, both of which had opened an ineffective fire upon her. The extreme range—in excess of —made the gunfire from both sides so ineffective that "Yankee" broke off the engagement and resumed her patrols between Casilda and Cienfuegos. The auxiliary cruiser continued her blockade of that stretch of the Cuban coast until 24 June, when her dwindling supply of coal forced her to head for Key West. "En route" to that base, she visited the Isle of Pines where she captured and destroyed five Spanish fishing vessels on the 25 June.