While steaming generally south on 29 April 1918, she sighted a sail bearing almost due west whose hull was down below the horizon. By the time the destroyer had swung around to an intercepting course, the sail had disappeared. While the destroyer steamed toward the estimated position of the sail, she searched for evidence of a submarine. After covering westward, she came upon an area marked by a number of small oil slicks. "Wainwright" chose the most promising of the slicks and dropped four depth charges. She then commenced another fruitless search which ended at midnight when she received orders to return to Queenstown.