"Schlesien" served with the High Seas Fleet through the first two years of the war. At the outbreak of the conflict, the ship was deployed to guard the German Bight. She then rejoined the High Seas Fleet to support the battlecruisers that bombarded Scarborough, Hartlepool, and Whitby on 15–16 December 1914. During the operation, the German battle fleet of 12 dreadnoughts and 8 pre-dreadnoughts came to within of an isolated squadron of six British battleships. Skirmishes between the rival destroyer screens convinced Admiral Friedrich von Ingenohl that he was confronted with the entire Grand Fleet, and so he broke off the engagement and went back home. Two fruitless fleet advances followed on 17–18 and 21–23 April 1915. Another followed on 17–18 May, and another on 23–24 October. In March 1916, "Schlesien" was employed as a target ship for U-boats. On 24–25 April, "Schlesien" and her sisters joined the dreadnoughts of the High Seas Fleet to support the battlecruisers of I Scouting Group on a raid of the English coast. While en route to the target, the battlecruiser was damaged by a mine. The remaining battlecruisers conducted a short bombardment of the ports of Yarmouth and Lowestoft. The target's visibility was poor, so the operation was soon called off before the British fleet could intervene. Squadron exercises in the Baltic followed from 11 to 22 May.