Like all other pre-dreadnoughts built at the turn of the century, Hessen was quickly made obsolete by the launching of the revolutionary HMS Dreadnought in 1906; as a result, she saw only limited service with the German 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.

Jutland revealed how inadequate pre-dreadnoughts like Hessen were in the face of more modern weapons, so she and the rest of II Squadron ships were withdrawn from service with the fleet.

[1][2] Though the Braunschweig class marked a significant improvement over earlier German battleships, its design fell victim to the rapid pace of technological development in the early 1900s.

[5] Hessen's armament consisted of a main battery of four 28 cm SK L/40 guns in twin-gun turrets,[b] one fore and one aft of the central superstructure.

The year was spent conducting squadron and fleet training exercises, including a summer cruise in July and August to Norwegian waters.

After returning, Hessen went to Swinemünde in early August, where Czar Nicholas II of Russia met the German fleet in his yacht Standart.

This year, the maneuvers were delayed to allow for a large fleet review, including 112 warships, for Kaiser Wilhelm II in the Schillig roadstead.

His tenure as fleet commander was marked with strategic experimentation, owing to the increased threat posed by the latest underwater weapons like submarines and naval mines, and to the fact that the new Nassau-class battleships were too wide to pass through the Kaiser Wilhelm Canal.

[10] Another fleet review was held during the exercises for a visiting Austro-Hungarian delegation that included Archduke Franz Ferdinand and Admiral Rudolf Montecuccoli.

[17] In February, during the very cold winter of 1911–1912, Hessen was employed as an emergency icebreaker in the Little Belt to rescue ships that were threatened by the heavy ice.

[10] In mid-1912, due to the Agadir Crisis, the summer cruise only went into the Baltic to avoid exposing the fleet during the period of heightened tension with Britain and France.

The year 1914 began quietly, with the only event of note being Hessen's visit to Sonderburg on 2 May to participate in the 50th anniversary celebrations commemorating the Battle of Dybbøl of the Second Schleswig War.

[19] As part of this process, Hessen was scheduled to be withdrawn into the reserve on 26 August 1914, with her place in II Squadron taken by the new dreadnought König, but the rising tensions in Europe during the July Crisis, which led to the outbreak of World War I, interrupted that plan.

Following Germany's entry into the war in early August, Hessen and the rest of the squadron were sent to the Altenbruch roadstead to support the defense of the German Bight at the mouth of the Elbe.

During the night of 15–16 December, the German battle fleet of twelve dreadnoughts and eight pre-dreadnoughts came to within 10 nmi (19 km; 12 mi) of an isolated squadron of six British battleships.

Skirmishes between the rival destroyer screens convinced the German commander, Admiral Friedrich von Ingenohl, that he was confronted with the entire Grand Fleet, and so he broke off the engagement and turned for home.

Squadron exercises in the Baltic took place from 18 March to 1 April, and further short periods of maintenance in Kiel followed on 17–18 May, 29–30 May, and 4–26 June; during the last stay, she had supplementary oil-burning equipment installed for her boilers.

Hessen and the five ships of the Deutschland class formed II Battle Squadron, under the command of Konteradmiral (KAdm—Rear Admiral) Franz Mauve.

On 31 May, at 02:00 CET, VAdm Franz von Hipper's battlecruisers of I Scouting Group steamed out towards the Skagerrak, followed by the rest of the High Seas Fleet an hour and a half later.

[28] The six ships of II Battle Squadron, having fallen behind, could not conform to the new course following the turn,[29] and fell back to the disengaged side of the German line.

Mauve considered moving his ships to the rear of the line, astern of III Battle Squadron dreadnoughts, but decided against it when he realized the movement would interfere with the maneuvering of Hipper's battlecruisers.

[30] Late in the day, Hessen and the Deutschland-class ships performed a vital blocking action that covered the withdrawal of the German battlecruisers.

Gunfire from Hessen and Hannover during the latter incident nearly hit the light cruisers Stettin and München; Scheer ordered them to cease fire.

[20] The experience at Jutland proved that the pre-dreadnoughts of II Squadron were a hindrance to the more modern units of the fleet, and so the Admiralstab decided that the ships should be withdrawn from service, as their crews could be used more effectively elsewhere.

The next two years passed uneventfully, and in July 1928, Hessen visited Norway with Admiral Hans Zenker, the chief of the Reichsmarine, aboard.

During the tour, Hessen stopped in numerous ports, including Vigo, Alicante and Cadiz in Spain, Palermo and Syracuse in Sicily, and Venice, Italy.

Hessen paid a visit to Bergen and Sognefjord, Norway, in July 1934 before participating in what would be her final annual fleet maneuvers later that year.

The ship's superstructure was cut down nearly entirely; Hessen retained only a single funnel, a tower foremast, and the two armored barbettes for the main battery turrets.

[7] On 31 March 1940, Hessen acted as an icebreaker for the auxiliary cruisers Atlantis, Widder, and Orion, on their trip from Kiel to the North Sea.