"Hessen"s peacetime career centered on squadron and fleet exercises and training cruises. She was involved in two accidental collisions, with a Danish steamship in 1911 and a German torpedo boat in 1913. "Hessen" was slated to be withdrawn from service in August 1914, but the start of World War I in July interrupted that plan and she remained in service with the High Seas Fleet. She performed a variety of roles in the first two years, serving as a guard ship at the mouth of the Elbe, patrolling the Danish straits, and supporting attacks on the British coast, including the raid on Scarborough, Hartlepool and Whitby in December 1914 and the Bombardment of Yarmouth and Lowestoft in April 1916. The following month, "Hessen" was present at the Battle of Jutland, the largest naval battle of the war. In the last daytime action between capital ships on 31 May, "Hessen" and the other pre-dreadnoughts of II Battle Squadron covered the retreat of the battered German battlecruisers away from the British battlecruiser squadron.