SMS Derfflinger was a battlecruiser of the German Kaiserliche Marine (Imperial Navy) built in the early 1910s during the Anglo-German naval arms race. She was the lead ship of her class of three ships; her sister ships were Lützow and Hindenburg. The Derfflinger-class battlecruisers were larger and featured significant improvements over the previous German battlecruisers, carrying larger guns in a more efficient superfiring arrangement. Derfflinger was armed with a main battery of eight 30.5 cm (12 in) guns, compared to the 28 cm (11 in) guns of earlier battlecruisers. She had a top speed of 26.5 knots (49.1 km/h; 30.5 mph) and carried heavy protection, including a 30-centimeter (11.8 in) thick armored belt.
Derfflinger was completed shortly after the outbreak of World War I in 1914; after entering service, she joined the other German battlecruisers in I Scouting Group of the High Seas Fleet, where she served for the duration of the conflict. As part of this force, she took part in numerous operations in the North Sea, including the Raid on Scarborough, Hartlepool and Whitby in December 1914, the Battle of Dogger Bank in January 1915, and the Bombardment of Yarmouth and Lowestoft in April 1916. These operations culminated in the Battle of Jutland on 31 May – 1 June 1916, where Derfflinger helped to sink the British battlecruisers HMS Queen Mary and Invincible. Derfflinger was seriously damaged in the action and was out of service for repairs for several months afterward.
The ship rejoined the fleet in late 1916, though by this time the Germans had abandoned their strategy of raids with the surface fleet in favor of the U-boat campaign. As a result, Derfflinger and the rest of the High Seas Fleet saw little activity for the last two years of the war apart from patrol duty in the German Bight. The fleet conducted one final operation in April 1918 in an unsuccessful attempt to intercept a British convoy to Norway. After the end of the war in November 1918, the fleet was interned in Scapa Flow. On the order of Rear Admiral Ludwig von Reuter, the interned ships were scuttled on 21 June 1919 to prevent them from being seized by the Allied powers.