SMS Seydlitz was a 25,000-metric ton battlecruiser of the Kaiserliche Marine, built in Hamburg, Germany. She was ordered in 1910 and commissioned in May 1913, the fourth battlecruiser built for the High Seas Fleet. She was named after Friedrich Wilhelm von Seydlitz, a Prussian general during the reign of King Frederick the Great and the Seven Years' War.
Seydlitz represented the culmination of the first generation of German battlecruisers, which had started with the Von der Tann in 1906, and continued with the pair of Moltke class battlecruisers ordered in 1907 and 1908. Seydlitz featured several incremental improvements over the preceding designs, including a redesigned propulsion system and an improved armor layout. The ship was also significantly larger than her predecessorsshe was approximately 3,000 metric tons heavier than the Moltke class ships.
Seydlitz participated in many of the large fleet actions during the First World War, including the battles of Dogger Bank and Jutland in the North Sea. The ship suffered severe damage during both of these engagements; during the Battle of Dogger Bank, a 13.5 in (34.3 cm) shell from the British battlecruiser Lion struck Seydlitz's rearmost turret and nearly caused a magazine explosion that could have destroyed the ship. At the Battle of Jutland she was hit 21 times by heavy caliber shells, one of which penetrated the working chamber of the aft superfiring turret. Although the resulting fire destroyed the turret, the safety measures put in place after the battle of Dogger Bank prevented a worse catastrophe. The ship was also hit by a torpedo during the battle, causing her to take in over 5,300 metric tons of water, and her freeboard was reduced to 2.5 m. She had to be lightened significantly to permit her crossing of the Jade Bar. The ship inflicted severe damage on her British opponents as well; early in the battle, salvos from both Seydlitz and Derfflinger destroyed the battlecruiser Queen Mary in a matter of seconds. The ship also saw some limited action in the Baltic Sea, when she provided screening for the German flotilla that attempted to clear the Gulf of Riga in 1915.
As with the rest of the German battlecruisers that survived the war, Seydlitz was interned in Scapa Flow in 1918. The ship, along with the rest of the High Seas Fleet, was scuttled in June 1919, to prevent its seizure by the British Royal Navy. She was raised on 2 November 1928, and scrapped by 1930 in Rosyth.