She was commissioned on 22 September 1915 under the command of Kapitänleutnant Otto Wünsche.[20] During the war, Wünsche and U-70 sank one warship, the British sloop Rhododendron, and 53 civilian ships totaling 137,775 GRT.[21] Among the civilian ships was Southland,[21] at 11,899 GRT, one of the largest ships hit by U-boats during the war.[22] U-70 also damaged four ships of 20,369 GRT.