In real life, Seydlitz was a one-off battlecruiser born out of Imperial Navy Department requests for more battlecruisers to match the Royal Navy, with assistance from Admiral Alfred von Tirpitz. In particular, Seydlitz featured better armor and propulsion over her preceding battlecruisers.
She was commissioned in 1913, with her first crew that of Yorck's, having just been transferred to reserve. She participated in many fleet actions throughout World War I, especially the battles of Dogger Bank and Jutland, where she survived severe damage that would have otherwise sunk her (which explains one of her skills that grants her temporary immunity from being sunk in a sortie). Later, she would have been part of the Ten Go-style suicidal sortie of the German Navy's High Seas Fleet in late October 1918, but mutinies broke out that forced the cancellation of the sortie. A month later, the ship was interned in Scapa Flow with the rest of the High Seas Fleet and scuttled a year later to prevent them from being divvied up by the Allies.
