However , she sighted no wreckage and broke off attack to guard the torpedoed ship after more than 2 hours of searching .
She made six vigorous depth charge attacks and sighted first a periscope wake followed by an oil slick .
She sighted no wreckage and broke off attack to guard the torpedoed ship after more than 2 hours of searching .
She made six vigorous depth charge attacks and sighted first a periscope wake followed by an oil slick .