At 14.07 hours on 4 Jul, 1943, U-178 fired a spread of three G7e torpedoes at the Breiviken (Master Alf Vasdal), dispersed from convoy DN-50 off Portuguese East Africa. One torpedo hit on the starboard side between holds #1 and #2 after 134 seconds and caused the ship to sink by the bow wihtin three minutes, capsizing to starboard. Three crewmen, including the British radio officer, were lost out of the 34 crewmen and two gunners aboard. About 20 survivors were picked up from the sea by the U-boat, where the master was questioned by an officer who spoke very good Norwegian. The Germans had spotted another ship before attacking Breiviken, nevertheless they spent 30 minutes with the rescue operation and then head off after placing all survivors on rafts. U-178 did not catch the first ship sighted, but came across Michael Livanos and sank her at 18.30 hours.

The survivors of Breiviken later found two drifting lifeboats from their own ship, righted and bailed them. On 7 July, they reached the coast near Ponto Barra du False, where they were taken care of by the lighthouse keeper and his wife and were later sent to Durban.