At 17.21 hours on 3 February 1941 the unescorted Dione II (Master Robert Squirrell), a straggler from convoy SC-20 due to bad weather since 26 January, was bombed and slightly damaged by a German Fw200 Condor aircraft of I./KG 40 in 55°40N/14°23W. This attack was witnessed by U-93 which had spotted the steamer about five hours earlier and unsuccessfully attacked her with a G7e torpedo at 14.10 hours. At 23.00 hours, the U-boat tried to attack with gunfire but heavy seas prevented the use of the deck gun and they had to break off the attack after they were sighted and attacked with a single round from the stern gun of the steamer, only firing the 20mm AA gun in the short gun duel.

At 04.40 hours, U-93 attacked Dione II again after moonset, hitting the bridge with the first round from the deck gun and preventing the use of the stern gun with the AA gun. The ship stopped when a fire broke out amidships but the inexperienced gun crew still had difficulties to hit the vessel until the IWO personally manned the gun. At 06.00 hours, the ship sank by the bow after being hit at the waterline by 30 rounds northwest of Aran Island, Co. Galway. The U-boat had used 155 rounds for the deck gun and 60 rounds for the AA gun in this attack. The master, 28 crew members and one gunner were lost. Five crew members were picked up by the British steam merchant Flowergate and landed at Glasgow on 8 February.