At 02.54 hours on 15 May 1942 the unescorted Siljestad (Master Nils Kaltenborn) was hit on the port side under the bridge by one torpedo from U-156 and sank after 40 minutes about 420 miles northeast of Barbados. The ship had been spotted at 17.20 hours the day before and missed with the first two torpedoes at 20.45 hours and 01.55 hours. The crew abandoned ship in the two starboard lifeboats, but two men fell overboard and drowned. The U-boat then questioned the survivors and gave them the course to Barbados before leaving the area. The survivors were picked up after about 12 hours by Kupa, which also hoisted the lifeboats on her starboard side and took care of the survivors. It was planned to let them continue in the boats because the ship was heading for South Africa.

At 20.59 hours on 15 May, the now zig-zagging Kupa was torpedoed by the same U-boat, which had observed how the vessel stopped and assumed correctly that they picked up the survivors from Siljestad. All Norwegian survivors abandoned ship in their lifeboats and the boat of the master lost contact with the others that night, but spotted the illuminated Italian steam tanker Arcola, which was en route with a British control crew to Las Palmas. Three young British sailors were transferred to the tanker, while the remaining men continued in the lifeboat to Barbados, after having been given plenty of food and water. They reached Bridgeport on May 20. The other Norwegian lifeboat and those from the Yugoslavian ship made landfall after ten days in Venezuela and Barbados.