At 08.03 hours on 21 Sep 1943 the unescorted Cornelia P. Spencer (Master Elmer H. Kirwan) was hit by one torpedo from U-188 about 300 miles off the coast of Somalia, as she was proceeding on a nonevasive course at 8 knots. The torpedo struck on the port side at #5 hold, blew off the hatch cover, flooded the hold, broke the shaft and rendered the engines useless. U-188 surfaced 100 yards off the port quarter. The armed guards fired about 75 rounds with the two 3in guns (the ship was also armed with eight 20mm guns) and forced the U-boat to submerge. About 30 minutes later, a second torpedo struck on the port side at the after peak and ignited the after magazine, killed two crewmen and blew the after gun crew into the water. The blast also carried away the rudder and propeller. The vessel began to settle rapidly and the master ordered the ship abandoned. The surviving men of the crew of eight officers, 32 men, one Royal Navy radio operator and 27 armed guards left the ship in four lifeboats and two rafts. At 09.15 hours a third torpedo struck amidships on the port side and the Cornelia P. Spencer sank stern first after ten minutes.

The survivors transferred to the four boats and set sail on a westerly course. 34 survivors in two boats were picked up by HMS Relentless (H 85) the next afternoon. 16 men in another boat were later picked up by the British steam merchant Sandown Castle and landed in Aden. The remaining 16 men in the fourth boat landed on the coast of Somalia, about 12 miles north of Garad, 15 days after the attack.