Treaty powers, with some important exceptions. The final version of Plan Z expected to supply this fleet by 1948, assuming that war did not interrupt construction. Battleships represented the core of the fleet. Scharnhorst and Gneisenau were the first step of the project. Armed with 9 11” guns, the two light battleships gave German builders valuable experience with large, fast ships, experience that had dissipated since the First World War. Unlike the other major powers, the Germans had no large battleships to reconstruct during the interwar period. Bismarck and Tirpitz represented the next step in the evolution, and were designed in explicit rejection of the limitations of the Washington Naval Treaty. Although they carried only 8 15” guns, the Bismarcks displaced nearly 50,000 tons, well in excess of treaty limits.
In the mid-1930s, the Nazi government began to plan in detail for the reconstruction of German naval power. The destruction of the German High Seas Fleet at Scapa Flow remained central to the mythology of German betrayal and defeat in World War I; rebuilding the fleet would be a grand achievement worthy of the Nazis, but also in accord with long-term German foreign policy goals.
In March 1935, Adolf Hitler announced that Germany would no longer abide by the naval restrictions established in the Treaty of Versailles, which had drastically limited German construction. Berlin and London quickly came to a new agreement, the Anglo-German Naval Treaty, which would limit German construction to 1/3rd that of the Royal Navy (RN), and would establish Washington Naval Treaty style restrictions on ship size and gun caliber.
Even before Germany reached the limitations of the new treaty, Hitler and the senior naval command developed plans for abrogating the agreement. These construction programs went by a variety of names, but became known in their final form as Plan Z. If fully undertaken, Plan Z would have given Germany a world class navy by the late 1940s.
Plan Z envisioned the construction of a balanced fleet, built along similar lines to those of the Washington Treaty powers, with some important exceptions. The final version of Plan Z expected to supply this fleet by 1948, assuming that war did not interrupt construction.
Battleships represented the core of the fleet. Scharnhorst and Gneisenau were the first step of the project. Armed with 9 11” guns, the two light battleships gave German builders valuable experience with large, fast ships, experience that had dissipated since the First World War. Unlike the other major powers, the Germans had no large battleships to reconstruct during the interwar period. Bismarck and Tirpitz represented the next step in the evolution , and were designed in explicit rejection of the limitations of the Washington Naval Treaty. Although they carried only 8 15” guns, the Bismarcks displaced nearly 50,000 tons, well in excess of treaty limits.
Eventually, six “H” class battleships would have formed the core of the German battlefleet. The H class went through multiple design iterations, but the 1939 project represents the most realistic culmination of Plan Z. Essentially enlarged Bismarcks, the Hs would displace 55,000 tons and carry 8 16” guns in four twin turrets. This would make them competitive with most of the advanced battleships planned by the United States  and the United Kingdom, although German designers still suffered from a lack of practical experience with modern vessels.
This would have given Germany ten modern battleships to contest the RN, supplemented four fast, modern, 35,000 ton aircraft carriers. The Germans also planned to construct three “O class” battlecruisers of classic design, faster than the battleships but unable to match them in armor. These ships would have specialized in attacks on enemy cruisers and merchant vessels.
Plan Z also envisioned a broader array of support vessels. The three Panzerschiff (“pocket battleships) represented an effort to circumvent the Treaty of Versailles, creating powerful, effective, long-range raiding units instead of the coastal defense battleships that the Allies expected. Nevertheless, Plan Z projected the construction of twelve additional vessels, suggesting that the ships would conduct operations along the lines of traditional heavy cruisers, as well as long-distance commerce raiding. The plan also allowed for five heavy cruisers and a range of smaller vessels.
Plan Z would have resulted in a powerful fleet, but not one that could beat the world. In comparison, by the time Plan Z reached completion, the RN would have operated a fast squadron including five King George V class battleships, six Lions (45,000 ton battleships carrying 9 16” guns), HMS Vanguard, and three refurbished World War I battlecruisers. A slow battleship squadron of between three and seven modernized ships would have supplemented the fast wing. The RN also projected to have at least seven modern fleet carriers, plus several older reconstructed conversions. RN advantages in cruisers and smaller ships were even more substantial.
To be sure, the British had global responsibilities; the RN needed to face down the Italians in the Med, and the Japanese in East Asia. In the event, the RN did in fact need to fight (or deter) all three opponents, but projected construction still left the Germans considerably behind the British.
Perhaps more importantly, the U.S. Two Ocean Navy Act, passed in 1940, established a plan to create a fleet that would have dwarfed Plan Z; by 1948 the U.S. Navy would have operated something along the lines of seventeen modern battleships, six battlecruisers, and an enormous number of aircraft carriers and cruisers. The Germans were also aware of Stalin’s plan to expand the Soviet Navy , although it’s unclear how seriously the Germans took this threat; the Russians faced dramatic geographic and industrial constraints that limited the effectiveness of their fleet operations.
The Germans understood this long-term deficiency, exacerbated by German geographic disadvantages. In part because of this, Plan Z still placed a strong value on commerce raiding. The Panzerschiff would provide a world-wide surface threat to Allied commerce, while squadrons consisting of battleships, aircraft carriers, and battlecruisers would specialize in convoy attack.
The Final Salvo:
Plan Z was destined for failure. When war began, Germany cancelled or delayed almost all of the major surface construction programs, completing only Bismarck and Tirpitz. The Kriegsmarine decided, almost certainly correctly, than U-boats represented a more effective threat to Allied commerce than squadrons of capital ships. Indeed, had the Nazi government rejected Plan Z entirely in favor of smaller raiders and U-boats, Germany undoubtedly would have been better prepared to wage World War II when it came. And even if Germany had prevailed in World War II, Plan Z would have left the Reich with a battleship heavy, carrier light force that would have matched up poorly with the modern U.S. Navy. Nevertheless, the prospect of German battleships, carriers, and battlecruisers fighting spectacular convoy battles against the RN and the U.S. Navy continues to spark the imagination.