 On 27 March at 07 : 20 Tynedale reported a U @-@ boat on the surface and opened fire . The two escort destroyers left the convoy to engage the U @-@ boat , later identified as U @-@ 593 . The U @-@ boat promptly <unk> and was unsuccessfully attacked by depth charges . The two destroyers returned to the convoy at 09 : 00 . 
