 Wainwright charged to the attack , but the submarine submerged almost immediately . Upon reaching the spot where the submarine had been , the warship located an oil slick and began dropping depth charges which failed to achieve positive results . Approaching darkness and the necessity of escorting an Admiralty oiler forced Wainwright to break off her attack . After she shepherded the oiler to safety , she returned to the area of her attack and patrolled throughout the night , but the submarine had apparently retired from the neighborhood . 
