At 09.30 hours on 1 Dec, 1939, the neutral and unescorted Arcturus (Master Nicolai Ludvik Engene) was hit on the port side in the bow by one torpedo from U-31 and sank within three minutes east of Scotland. The master and eight crew members were lost. The ship had been spotted at 05.50 hours with lights set, but without visible national markings and missed with a first torpedo at 09.27 hours.
Both lifeboats went down with the ship and the eight survivors rescued themselves on two rafts that floated free after the ship sank. They tied the rafts together and were spotted the next morning by a British aircraft which directed the Danish steam merchant Ivar to their location. The survivors were picked up and landed at Fredrikshavn, Denmark.