SMS Mainz was a Kolberg-class light cruiser of the German Kaiserliche Marine (Imperial Navy) during the First World War.

The primary objective during their design process was to increase speed over the earlier vessels; this required a longer hull to fit an expanded propulsion system.

The ship carried a pair of pole masts with platforms for searchlights, one directly aft of the conning tower, and the other closer to her stern.

[2] Mainz was ordered under the contract name Ersatz Jagd and was laid down in September 1907 at the AG Vulcan shipyard in Stettin.

On 6 June, Mainz joined the reconnaissance force of the High Seas Fleet, taking the place of the light cruiser Danzig.

Mainz and the rest of the fleet received British and American naval squadrons in Kiel in June and July.

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

[8][9] 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.

[5] The High Seas Fleet again hosted a British squadron in June 1914, days before the assassination of Archduke Franz Ferdinand.

[11] After the outbreak of World War I at the beginning of August 1914, the cruiser Arcona was the only vessel on station to guard the German Bight.

The cruisers were divided with the torpedo boat flotillas and were assigned to rotate through nightly patrols into the North Sea.

As part of this operation, Mainz conducted a patrol on the night of 16 August with the VIII Torpedo-boat Flotilla, without incident.

[13] On the night of 21–22 August, Mainz provided distant support to a patrol of torpedo boats that inspected fishing vessels in the Dogger Bank.

[14] The British forces began to leave port on the evening of 26 August, beginning with the submarines assigned to the operation.

[15] On the morning of 28 August, Mainz was at anchor in the mouth of the Ems; her sister Cöln, the flagship of Konteradmiral (Rear Admiral) Leberecht Maass was re-coaling in Wilhelmshaven, Ariadne lay in the entrance to the Weser.

In the ensuing Battle of Heligoland Bight, Stettin engaged the British force first, and was quickly reinforced by Frauenlob.

The pursuing British cruisers scored several hits, but by 12:55, Mainz had escaped under cover of a dense smoke screen.

Another British cruiser, Fearless, and six destroyers, appeared on Mainz's port side, however, and attacked the fleeing German ship.

Winston Churchill, then the First Lord of the Admiralty, informed Tirpitz via the United States' embassy in Berlin that his son survived the battle and had not been injured.

[20] In August 2015, members of the Dutch sport-diving club Duikteam Zeester dove on Mainz's wreck and retrieved a variety of prosaic artifacts, including a sextant, the engine telegraph, and a sight for one of her guns.

Their actions provoked criticism from German sources, who noted that the wreck was a war grave containing the remains of 89 crew members and thus should not be disturbed.