The Z-Plan was Germanys fleet building program started shortly before World War 2.
In the mid 1930s a major discussion about a new fleet program started in Germany. There were two major opinions, what kind of program should have been chosen. One plan was focused on a large submarine fleet and a relatively small surface fleet for coast protection, this plan was preferred by the U-Boat fraction in the Kriegsmarine command. The other alternative was a mixed fleet of various surface ships and a much smaller U-Boat fleet, quite similar to the Imperial Navy in World War I or the British Royal Navy. In the end, this plan was chosen as the new fleet building program, after several modifications it was called the "Z-Plan".
According to this plan, the German Kriegsmarine should have grown to about 800 units, consisting of 13 battleships and battlecruisers, 4 aircraft carriers, 15 Panzerschiffe, 23 cruisers and 22 so called "Spähkreuzer" which were basically large destroyers. In addition to this many smaller vessels should have been build.
Those ships should have been build between 1939 and 1946, in this time, the personal of the Kriegsmarine should have been enlarged to 201.000 men and over 33 billion Reichsmark should have spend for building the new units.
This project never got reality. Its very questionable that the German industry would have had the resources for such a construction program and that the other European Nations would stood still and not react to this program. The realization of the Z-Plan started on January 29th, 1939. Two H-Class battleships were laid down, three months later Germany quit the the fleet treaty with England and the dream "No more war against Britain" was gone.
But only four months later Germany attacked Poland and work on all Z-Plan projects was stopped. During the next months, all incomplete ships of the Z-plan were scrapped and the material was used to build additional submarines.