 The Prize was lost on its fourth patrol , Sanders having been promoted to lieutenant commander . On 14 August 1917 , UB @-@ 48 spotted the Prize . The Q @-@ ship was recognised by the captain of the U @-@ boat , who had been warned by the survivors of U @-@ 93 and did not approach the Prize too closely . Instead , it remained submerged and fired two torpedoes into the sailing ship , blowing her to pieces . Rescue craft were unable to find a trace of her crew when they arrived in the area , long after the U @-@ boat had escaped . 
