Short answers, pulled from the story.
Plan Z was Germany's naval expansion program, ordered by Adolf Hitler in early 1939, to build a fleet of 797 ships capable of challenging the Royal Navy. Approved on the 27th of January 1939, the program was intended to be completed by 1948 at a total cost of 33 billion reichsmarks. It was cancelled after World War II broke out in September 1939 before any of the new ships could be built.
Plan Z called for a total of 230 new and existing ships, including 10 battleships, 3 battlecruisers, 4 aircraft carriers, 15 panzerschiffe, 5 heavy cruisers, 13 light cruisers, 22 scout cruisers, 68 destroyers, and 90 torpedo boats. When completed in 1948, the German fleet was projected to number 797 ships in total.
World War II began on the 3rd of September 1939, less than eight months after Hitler approved Plan Z, leaving no time for construction. Only two H-class battleships were laid down before the outbreak of war, and both were cancelled shortly after. Germany redirected manufacturing capacity to more urgent wartime needs, and the entire program was shelved.
Plan Z prioritized surface ships over submarines, leaving Admiral Karl Dönitz with only a few dozen U-boats at the outbreak of war. Dönitz calculated he needed 300 submarines to win a commerce war against Britain, a figure that was not reached until 1943, by which time the North Atlantic campaign had already been lost. The funds spent on battleships like the Scharnhorst and Bismarck classes could instead have built more than a hundred additional Type VII U-boats.
Plan Z was developed under Grand Admiral Erich Raeder, who favored long-range surface raiders to attack British trade rather than a direct fleet confrontation. Hitler overruled Raeder's earlier drafts, called Plan X and Plan Y, demanding a balanced battle fleet centered on battleships. Admiral Karl Dönitz simultaneously pushed for investment in submarines and unrestricted submarine warfare, a strategy that was sidelined by the surface-fleet priority of Plan Z.
The Kriegsmarine's projected fuel needs under Plan Z would have risen from 1.4 million tons in 1936 to approximately 6 million tons annually by 1948, and Germany would have needed to build around 9.6 million tons of fuel storage just for a single year of wartime reserves. Germany's projected domestic oil production by 1948 was less than 2 million tons, a figure that also had to supply the army, air force, and civilian economy. Planners never seriously addressed this gap before the plan was approved.