After the London Treaty signing, the pressure applied by the political leadership on the Reichsmarine grew constantly larger. The U-boat arm stood somewhat aside from this; they faced other problems. And, with the exception that the number of outfitting yards was increased to nine, Plan Z had no further effect on the U-boat building or design. Instead, the U-boat arm had to care about yard capacities and the specialists for it. Building U-boats was manpower intensive. With few exceptions, all of the pre-war U-boats were built at Deschimag, Bremen or Germania, Kiel.
The design of the Type I a, II a-d, III, III mod., IV, V, VI, VII and IX U-boats was done at the MA in the early 30's under a cover project named "Entwicklungsaufgaben auf dem Gebiete des Motoren-Versuchsboot-Wesens", which can be translated to something like "Research on engine-trial vessels". During this period only the Types I a, II a-d, VII and IX were built. But, it is interesting to see that during this time Project IV displayed the first thoughts on having "milk-cows" type U-boats and Project V considered the "fast attack submarine" based on the ideas of Hellmuth Walter.
The construction methods used for building these new U-boats was done roughly in the same manner as one did it in WWI. This process was very lengthy, because the hull was completed first and then everything for the interior, including the engines, had to make its way inside the hull through the narrow hatches. During this period, it took about 10 months to build a Type VII U-boat.
With the outbreak of WWII, the Plan Z became obsolete. The leadership of the Reichsmarine decided very early during the war to increase the building of U-boats and many shipyards were modified to do this. The design efforts increased also, but mainly these were confined to variations of the types already in service, the Type VII and Type IX.
In the late summer of 1939 the MA was rearranged into the K-Amt and the Department of Armament (DoA) was set up, led by Mr. Todt (better known as the creator of "Organization Todt"). His duty was the coordination of the armament industry, but he was killed in a plane crash 1942. His successor was Albert Speer who was appointed Reich Armaments Minister.
From 1940 – 1943 the manufacturing time for U-boats was notably decreased. The shipyards adopted the system of pre-fabrication, first used on a mass basis by the US Navy during WWI for the construction of merchant vessels. But this was only done with the hull itself. Outfitting was still done as before. About 19 shipyards assembled between 24 to 26 U-boats per month of Types VII c, IX c and IX d. Using this same system to build the new, and quite larger, Type XXI would have meant a build rate of approximately 20 U-boats per month. This was considered to be too low by the Naval High Command (OKM = Oberkommando der Marine). An alternative construction method was needed to get the higher numbers needed.
As I said above, the so-called "Walter-subs" were a subject of studies from the early (official) beginning days of the U-boat arm. This propulsion system was constantly experimented with, but the hydrogen-peroxide fuel (H2O2 and Walter-turbine) proved to be very dangerous and mechanically unreliable with no end in sight. A design breakthrough came when someone suggested eliminating the Walter-engine and instead simply copying the "traditional" (diesel) engine set-up but use larger E-engines (electric) and batteries. So, that was the transition from Project XVIII to Project XXI. This occurred in early 1941. At that time, everyone expected that the war would end in a few months, so there was no urgency to get this design off the drawing boards. However, by 1943, with the war still going on and now with Russia and the US as enemies, they thought differently. The design was dusted off and rushed to completion in late 1943.
The year 1943 saw some major changes in the Navy as a whole as well as the U-boat arm. Adm. Dönitz was appointed as the successor to Adm. Raeder when the latter resigned. Despite the fact that Adm. Dönitz saved the large surface ships from the scrapyard, it was plain to see that he wanted greater progress for "his" U-boats. He managed to secure the highest priority for the U-boat construction from the Führer, but he also knew that Hitler was very generous with such orders (for example, a few weeks previously panzer production had earned the same highest priority level). So, Adm. Dönitz did what no one would have ever expected. He removed the K-Amt organization from U-boat production. Instead, he gave the responsibility for their manufacture to Albert Speer and his Department of Armament. In effect, Adm. Dönitz traded influence for output. The design of the new Type XXI, XXIII and Type XXVI U-boats was completed, what was important now was to get them built as quickly as possible.
K-Amt, i.e., Department K IU, was relegated to working only on the requirements for Types VII C, VII D and VII G (which never entered construction). Soon after this time, further development of Type VII C 42 was stopped. The rest of the K-Amt was also reduced to only working on new designs.
Everything to do with building and maintaining ships, vessels or subs was given to the DoA. The new organization inside DoA was named "Hauptausschuß Kriegsschiffbau" (Main Board for Warship Construction) and included 9 special committees consisting of 62 working groups. These were organized as follows:
| Committee | Working groups |
|---|---|
| U-boats | 5 |
| Warships | 9 |
| Wooden ships | 6 |
| Merchant ships | 5 |
| Coastal and inland vessels | 5 |
| Amphibious and special ships | 7 |
| Propulsion and Boilers | 8 |
| Ship Diesel engines | 4 |
| Repairs and Refits | 13 |
Additionally, there were also planned to be eight so-called "Länderbeauftragte", local managers in the occupied countries responsible for the executing the orders of the DoA. This was never effectively implemented due to the lack of resources and to a far larger degree the progress of the Allied armies as they overran those territories.
From the viewpoint of K-Amt, the Department of Armament turned the world upside down. Albert Speer promised to Dönitz an output of 40 Type XXI and Type XXIII U-boats a month. The man put in charge of this effort was Otto Merker, a managing director of Klöckner-Humbold-Deutz. Merker's background was mainly in the manufacture of trucks and fire-engines, but he had the reputation of being a genius in organizing manufacturing processes.
Merker's solution to Speer's promise was to set up a central engineering bureau out of a few hundred specialists that he took from yards and the steel industry. He decided that these new U-boats should be built like the US "Liberty-ships" in pre-fabricated sections that were then joined together as a final assembly step. The U-boats were subdivided into sections, with the Type XXI having 8 sections, the Type XXIII 4 sections and the Type XXVI 8 sections. Merker then created three general building "areas", each including one assembling shipyard, 1 – 8 section yards and 30 to 40 suppliers (steel, machinery, electric gear and so-on). These three building stages were as follows:
The first built the pressure and external hull sections, bulkheads and other hull work. The plating and frames were received at the yards pre-cut and set to the proper shape by the steelmakers. About 32 shipyards and structural engineering firms were involved were engaged in this stage.
The sections were then transported, generally by water, to other firms, some 16 in number. In this second stage, all wiring, pipework and main and auxiliary engines were installed.
The third stage consisted of three shipyards welding together the completed sections on the building slip, carrying out dockyard testing and then turning the boats over to the Navy.
The building areas were as follows:
| Area | Submarine(s) produced | Assembly yard | Section yard(s) | |
|---|---|---|---|---|
| # | Name | |||
| "Danzig" | Type XXI | F. Schichau, Danzig |
|
|
| "Hamburg" |
|
Blohm & Voss, Hamburg |
|
|
| "Bremen" | Type XXI | Deschimag, Bremen | 1 | Howaldt, Hamburg |
| 2 | KMW, Wilhelmshaven | |||
| 3 | Bremer Vulkan | |||
| 4 | Flender-Werft Lübeck | |||
| 5 & 6 | Bremer Vulkan | |||
| 7 | Seebeck, Wesermünde | |||
| 8 | Deutsche Werke, Kiel | |||
This production line proved to be quite effective, in 1944, a monthly outlet of 30 type XXI and 8 type XXIII was reported. For comparison, the building of a Type IX U-boat (nearly similar in displacement to the Type XXI) took an average of 27 weeks while that of a Type XXI took only 7 weeks. All in all, the production rate was nearly four times faster. The total number of U-boats built under these methods looks like this:
| Submarine | Officially ordered | Under construction | Launched | Delivered |
|---|---|---|---|---|
| Type XXI | 576 | 200 | 165 | 145 |
| Type XXIII | 150 | 100 | 85 | 73 |
In evaluating these figures one should consider that the yards were virtually shutdown after January 1945 as the Allies started to overrun the production areas.
The U-boat projects of Marineamt (MA) and K-Amt (as far as I was able to discover them)
| I A | Hochsee-Tauchboot (Highsea Diveboat) |
| II A-D | Hochsee-Tauchboot (Highsea Diveboat) |
| VII - VIIc - VIIc/42 | C/42 Hochsee-Tauchboote (Highsea Diveboat) |
| VIId | Minen-Uboot (Mine sub) |
| VIIf | Transport-Uboot (transport sub) |
| IX - IXd | Tauchboot für ozeanische Verwendung (Ocean Diveboat) |
| Xa - Xb | Minen-Uschiff für ozeanische Verwendung (Ocean Mine U-boat) |
| XI | U-Kreuzer (Tauchkreuzer) (Sub-Cruiser) |
| XII | U-Schiff-Projekt (Flotten-Uboot) (Fleet sub) |
| XIII | Kleines Uboot, nur Projekt (small U-boat only project) |
| XIV – XVI | Versorgungs-Uschiffe für ozeanische Öltransporte (Maintenance ocean subship) |
| V 80 | Versuchs-Uboot (Test sub) |
| V 300 | Versuchs-Uboot (Test sub) |
| Wa 201 | Versuchs-Uboot (Test sub) |
| Wk 202 | Versuchs-Uboot (Test sub) |
| XVII | Versuchs-Uboot (Test sub) |
| XVIII | Walter-Uschiff (Walter sub) |
| XIX – XX | U-(transport)-Frachtschiffe (merchant subs) |
| XXI | Unterseeschiffe (subships) |
| XXII – XXIII | Unterseeboote für Mittelmeer und küstennahe Verwendung (subs for the Mediterranean Sea and coastal areas) |
| XXIV | Walter-Uschiff Projekt (Walter subship project) |
| XXV | Elektro-Unterseeboot Projekt für Küsteneinsatz (Coastal E-sub project) |
| XXVI | Hochsee-Walter-Uboot (highsea Walter sub) |
| XXVI A | Alternativ-Projekte zu XXVI (alternatives to XXVI) |
| XXVI B | Alternativ-Projekte zu XXVI (alternatives to XXVI) |
| XXVI E1 | Alternativ-Projekte zu XXVI (alternatives to XXVI) |
| XXVI E2 | Alternativ-Projekte zu XXVI (alternatives to XXVI) |
| XXVII | Kleinst-Uboot "Hecht" (mini-sub) |
| XXVIIB | Kleinst-Uboot "Seehund" (mini-sub) |
| Projekt K | Kleines Tauchboot für Naheinsatz (Diesel-Kreislaufantrieb) (small sub for close combat, diesel recirculation) |
| XXVIII | Projekt, Reines Unterseeboot für Mittelmeereinsatz (indirekter Walterantrieb) (Walter sub for Mediterranean Sea) |
| XXVIII F | Projekt, "Schwertwal" (project) |
| XXIX A – D | Studienprojekte zur SKL-Forderung "halbe XXI-Maschinenanlage" (project-study) |
| XXIX F/GK/H | Studienprojekte zur SKL-Forderung "halbe XXI-Maschinenanlage" (project-study) |
| XXIX K1 – 4 | Vergleichsentwurf zu XXIX A – D (comparative design to XXIX A-D) |
| XXX | w. v. (as above) |
| XXXII | Projekt, Kleinst-Uboot nur Batterie (minisub project, battery only) |
| XXXIII | Projekt, Küsten-Uboot mit Dieselkreislaufantrieb (minisub project, diesel recirculation) |
| XXXIV | Projekt, wie XXXIII jedoch ohne Turm (project similar to XXXIII but without sail) |
| XXXV | Projekt, Uboot für reine Sauerstoffverwendung (project, sub for Oxygen use) |
| XXXVI | w. v. (as above) |
- 2 December 1999
- Updated