Between 09.51 and 09.52 hours on 13 March 1943, U-68 fired three torpedoes at a freighter and a tanker in convoy GAT-49 in clear weather and a moonless night about 170 miles northwest of Curaçao and hit the Cities Service Missouri with one of them. The U-boat then fired a spread of two torpedoes in a second attack on convoy at 10.24 hours, hitting the Ceres with both and afterwards finished off the damaged tanker behind convoy.

The Cities Service Missouri (Master John H.B. Morton) in station #23 was the last ship in the second column and was struck by one torpedo at the stem on the starboard side. The explosion ripped a ten foot hole in the side and vented upward, damaging the bridge and wheelhouse. The vessel stopped to determine the damage and the master thought she could be saved if they shift the ballast. At 11.02 hours, a second torpedo struck the port side in the engine room and demolished the engines, just as they had brought the tanker on even keel. U-68 was then spotted on the surface about 1300 yards from the tanker and the armed guards (the ship was armed with one 5in and two .50cal guns) fired three rounds at the U-boat, which was not hit but forced to crash dive. By this time water had risen to the base of the gun and 30 minutes later the master ordered the crew to abandon ship. All eight officers, 35 crewmen and eleven armed guards left the Cities Service Missouri in three lifeboats and one raft. The U-boat left the area without finishing off the tanker after one torpedo missed at 11.29 hours and another became a circle runner at 11.45 hours. The ship eventually plunged stern first with her bow straight in the air at 12.40 hours. USS Biddle (DD 151) (LtCdr T.A. Torgerson, USN) picked up the survivors three hours later, but the boatswain drowned trying to get on the destroyer and a machinist died of wounds and burns on board. The destroyer then rescued the survivors from Ceres and on 14 March landed them all in Willemstad, Curaçao.