sentences:  In May in an attack on SC 129 B2 sank "U-186" and damaged "U-402" and "U-223" for the loss of two ships.A series of uneventful convoys followed, as the U-boat arm withdrew from the North Atlantic after Black May, a state of affairs which continued until the end of the year.During this period the group had escorted over 30 convoys, totalling over 900 ships of which only 10 were lost.