At 06.08 hours on 5 June 1942 the unescorted and unarmed Delfina (Master Jake Jacobs) was hit by one G7e stern torpedo from U-172 while steaming on a non-evasive course at 9.5 knots about 130 miles north-northwest of San Juan, Puerto Rico. The U-boat had followed the ship for seven hours and had already fired three single torpedoes during the chase, but all malfunctioned due to different causes: one G7a torpedo fired at 03.22 hours went straight to the bottom, another G7a fired at 04.13 hours became a tube runner and missed and one G7e torpedo fired at 05.07 hours was a dud. The fourth torpedo then struck on the port side between the #3 hold and the boiler room and caused the ship to sink bow first after 20 minutes. The radio operator sent a distress signal and received an acknowledgment from a San Juan radio station. The inexperienced crew of eight officers and 23 men abandoned ship in a chaotic manner in moderate seas during a dark night. The port lifeboat had been destroyed by the explosion and the only remaining boat was launched, but the men put it into the water in such a way that it filled half-way with water. The master was in the boat and ordered its occupants to pull away quickly in fear of being shelled without waiting for the others that were still aboard. The remaining survivors, among them the first and third mate and the radio operator, had to jump into the water when the ship sank and swam to four rafts that had been released by the cook or clung to wreckage. The U-boat was seen to surface nearby, but the Germans already identified the ship from her radio message and left without questioning or helping the survivors.

One officer and one crewman on watch below had been killed by the explosion and one officer and one crewman drowned when the ship sank. The twelve survivors left behind at the sinking location gathered together on two rafts, were spotted by an aircraft the following morning and picked up by the American patrol craft USS YP-67 (Lt(jg) Thomas H.P. Whitney, USN) about 16 hours after the attack in position 20°24N/67°20W. Three of them were slightly injured and were hospitalized after the survivors landed at San Juan. On 9 June, the master and the 14 crew members in the lifeboat made landfall at Montecristi, Dominican Republic.