At 23.03 hours on 27 Oct, 1942, U-436 fired a torpedo at the convoy HX-212, heard a detonation after 59 seconds and observed the hit on the Frontenac. Five minutes later a spread of three torpedoes was fired and detonations were heard after 1 minute, 1 minute 16 seconds and 2 minutes 24 seconds. The third torpedo sank the Sourabaya and the fourth damaged the Gurney E. Newlin, both hits were observed by Seibicke. At 23.11 hours, U-436 fired the stern torpedo and reported another ship damaged, but this is not confirmed by Allied sources.

The Frontenac was torpedoed first, loosing a part of the foresection and evaded the Sourabaya, which was out of control after she had been torpedoed. The explosion caused a fire at the bow, which was extinguished by a big wave, but the bow settled so deep that the screw was out of the water and the tanker stopped in the rough seas. The mate Arntzen volunteered to going down in the foreward tanks to open the valves and start the pumps. Until the next afternoon they had lost about 1000 tons of oil, but she was able to continue the voyage alone at 4 knots. After the forward tanks were empty she could resume at her normal speed. When the Frontenac was about 50 miles west of Ireland with a extremely tired master on the bridge, who did not sleep in a bed for seven days and nights, a large convoy appeared in front of them and a destroyer came alongside to identify the vessel, but left later to continue with the convoy, which was part of the Operation Torch, the invasion of North Africa.
On 4 November, the badly damaged Frontenac reached Ramlash. The tanker was fitted with a new bow section and returned to service on 5 Mar, 1943.

The master, William Thorsen, had already experienced another sinking, when his earlier ship, the Moira, was sunk by U-158 (Rostin) on 17 Jun, 1942.