 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 10 nautical miles ( 19 km ) 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 . 
