The Ersatz Yorck class was a group of three battlecruisers ordered but not completed for the German Kaiserliche Marine (Imperial Navy) in 1916. The three ships had originally been ordered as additions to the Mackensen class, but developments abroad, particularly the British Renown-class battlecruisers, led to the navy re-designing the ships. The primary change was an increase of the main battery from eight 35-centimeter (14 in) guns to eight 38 cm (15 in) weapons. Work on the first ship had already begun by the time the navy decided to re-design the ships, so the design staff was constrained by the need to use the material already assembled.
The name derived from the fact that the lead ship was intended as a replacement (German:ersatz) for the armored cruiser Yorck, lost to mines in 1914, and it had been ordered under the provisional Ersatz Yorck. The other two ships, Ersatz Gneisenau, and Ersatz Scharnhorst, were considered to be replacements for the armored cruisers Gneisenau and Scharnhorst, both of which had been sunk at the Battle of the Falkland Islands, also in 1914.
As with the Mackensens, the three ships of the Ersatz Yorck class were never completed. This was primarily due to shifting wartime construction priorities; U-boats were deemed more important to Germany's war effort later in the war, and so work on other types of ships was slowed or halted outright. The lead ship, Ersatz Yorck, was the only vessel of the three to have begun construction, though she was over two years from completion by the time work was abandoned. The ship was broken up on the slipway and machinery that had been assembled for Ersatz Gneisenau was installed in the first four Type U 151 U-boats. Nevertheless, the work that had gone into the Ersatz Yorck design was not a wasted effort; when the design staff began work on the Scharnhorst-class battleships in the 1930s, they used the plans for Ersatz Yorck as a starting point.