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 torpedoes struck Ceres (Master Hendrik Cornelis Elderenbosch) on the starboard side, the first underneath the bridge and the second in #5 hold. The explosions set the cargo stored in #3 and #5 holds on fire and completely smashed the wireless room, charthouse and wheelhouse. The crew of 34 men, two gunners (the ship was armed with one 3in gun) and three passengers immediately began to abandon ship in both starboard lifeboats as an increasing list made it impossible to use the ones on the port side. Alarmed by the previous attack the most men managed to leave the Ceres just before she buckled up and sank two minutes after being hit. Two crew members were lost. At dawn the survivors in the two boats searched the area for others who had jumped overboard, picking up a number of men out of the water and from the four rafts that had been released. USS Biddle (DD 151) (LtCdr T.A. Torgerson, USN) found a survivor from Ceres in the water after picking up the survivors from Cities Service Missouri and subsequently rescued 36 more from the lifeboats and rafts about six hours after the sinking. On 14 March, the destroyer landed all survivors in Willemstad, Curaçao.