H-class battleships and Z51 as diesel precedents

Some H-class battleship designs and the engines developed for Z51 show that large German marine diesels were part of historical design work. MAN's development includes the twenty-four-cylinder machinery discussed here. The counterfactual brings that effort forward and gives it a larger share of resources. Those projects provide a historical starting point, without establishing that the same machinery was ready throughout the early 1930s. Z51 is judged too late to affect the war as it actually unfolded.