The eighth and last war patrol that "U-30" was to undertake began on 5 August 1940, when she left Lorient for the North Atlantic. In 26 days, she travelled north of the British Isles, into the North Sea and entered the German port city of Kiel on 30 August 1940. During that time, she sank the Swedish vessel "Canton" on 9 August and the British steam merchantman "Clan Macphee" on 16 August 1940. Both of these attacks took place off the west coast of neutral Ireland. After these successes, however, "U-30" once again experienced engine trouble and was forced to end her patrol early, returning to Germany. Before she arrived, Lemp received word that he had been awarded the Knight's Cross of the Iron Cross for the boat's previous war patrols.