Was there a German re-urbanization plan for after WWII?

Q Was there a Germany-wide re-urbanization plan for after the WWII?

Yes. One could say so. Although not in the sense that there was such one 'central' plan for the whole of Germany detailing every last little aspect for every city in the same way.

What we see instead is a general trend – perhaps a fad – with ample parallels between different cities that led to a slew of similarities. The guiding lines were largely shared and identical. Leading to a lot of continuity in ideas and personnel implementing them. Not one plan for all. But lots of similar plans in parallel with a largely shared vision.

This is the exact same kind of 'centralised planning' one might expect from grandiose nazi planners. Even those would account for broad strokes of similarity in outcomes, true, but while we expect a largely uniform trend from those guys, Linz would still look different from Nuremberg and both different from Hamburg or Berlin.

"…for after the WWII" implies that such a plan was devised before the end of that war. In contradiction to the stated goal of the question. And city planning with immense re-structuring was devised indeed in early nazi-times, by nazis, and after the war for large parts by those same nazis.

Which makes the next part of the question a bit moot:

Q I don't mean a hypothetical Nazi re-building plan, but a real implemented plan.

This is an artificial dichotomy and therefore a narrowed framing. Nazi plans that were implemented after the war don't count? Why not? Is this meant to transport: "were there any non-nazi plans that were also implemented after the war?"

Thus the point to emphasise is that nazi plans like "Germania" were not carried through, entirely. But since these plans were in a tradition of thought from long before the nazis were invented, and 'things' like the roads Heerstraße/Bismarckstraße/Straße des 17. Juni are still in place according to Speer's vision (not many of that plan are):

This meant the great 1930s demolition areas around the Reichstag for example remained open until very recently (late 1990s).

This connects also to the other Berlin difficulty resulting from its past: does building a new (now post ‘Fall of the Wall’) German capital in a hole created by Speer today mean you’re in some way completing his task? Perhaps this is why the new ‘Ribbon of Government’ buildings are designed to run at 90 to the Nazi orientation and directly through the site of the proposed Hall of the People (most of which is left as green space)?

Today’s new road and rail tunnels under the Tiergarten park are a final realisation of the urban design plans of Mächler, Speer, and Hitler a century ago. They are essential, but conveniently invisible.

Below ground, where many Nazi period constructions lay, only ca. 5 % was touched. This, and the fact that they are invisible, difficult and expensive to approach means there is still a Nazi underground world beneath Berlin, it’s just that few of us get to see it. Beneath the Tiergarten Park, roughly below the road opposite today’s Soviet memorial, are three tunnels that would have taken traffic on the new north-south axis underneath the existing east-west axis road widened by Speer in 1938-9. — Berlin Long Reads | Visions Of Germania

Berlin: Hitler's favourite architect and his Berlin legacy
Berlin: A road to Hitler's Germania

As outlined in this fine answer, a central guideline for urban development was issued in East Germany. That was heavily influenced by the Socialist interpretation of architectural modernity. In the West such a guideline or plan was almost superfluous, as most architects simply clung to their own interpretation of modernity, in this case largely a nazi one that only lost some of the more bizarre 'edges' and those monumental aspects using up too much concrete — and incorporated ever more cars into their thoughts and designs over the following years.

Thus the quest to find any urban design plans in West-Germany free of nazi legacy is an artificial one bound to fail. WP: Urban planning in Nazi Germany#Legacy

A note on terminology:

A "re-urbanization plan" seems to assume that Germany was somehow 'de-urbanised by certain events occurring around 1945?

That was certainly not really the case, any such things like Morgenthau plans not withstanding:

_{— Franz Rothenbacher & Georg Fertig: "Urbanisierung und Siedlungsformen", bpb.de, 28.1.2016.}

So we're left with pre-, mid- and post-war urban planning and city developments.

First, the general assumption as presented in question is of course quite true:

"The mechanical loosening up by bomb war and final battle now gives us the possibility of a generous organic and functional renewal"
_{— Hans Scharoun 1946 Berlin Magistrat}

While it may seem obvious that after two separate states were established on German soil that there could hardly be one general plan for two different countries, it is nevertheless astonishing to note the almost identical outlook n both of them:

In the middle of the Second World War, immediately after the bombing of large German cities, the first concepts for reconstruction were developed. Until 1958, these had determined the actual planning in the Federal Republic. But the founding of two German states in 1949 also led to a split in the guiding principles for urban development along the German-German border. […]

There was a broad consensus among urban planners and architects to use the destruction as an opportunity to implement long overdue reforms in urban planning, […] In the early days, the basic ideas were quite the same in East and West, explains Hartmut Häußermann: Away with chaos, away with confusion, radical reorganization of the city. Functionalism was considered the basic idea of the modern city on both sides.[…]
_{— Wiederaufbaupläne der Städte: Zwischen Funktionalismus und politischer Inszenierung}

As one particular exmpale of this personal and institutional continuity, we might look at Wilhelmshaven.

The Wilhelmshaven Urban Development Plan of April 1942, which Schneider presented together with Friedrich Heuer, concentrated the planning even closer to the Old Town, monumentalized the Kulturforum and extended it to the west around parade grounds and massive peripheral developments.[…]

With Hitler's decree on the preparation of the reconstruction of bomb-damaged cities on October 11, 1943, and the establishment of the task force for the reconstruction planning of destroyed cities by Albert Speer in December 1943, design goals developed again in the heavily bombed-out Wilhelmshaven.[…]

Immediately after Hitler's decree on the preparations for the reconstruction of bomb-damaged cities on October 11, 1943, city planning director Walter Temp contacted Wilhelm Wortmann of the LOB.

At the end of 1945, Helmuth Baur began preparatory work for a new economic plan, which was adopted by the Council in October 1947 as a preliminary economic plan. In addition, the Lower Saxony Office for State Planning and Statistics worked from the beginning of 1948 on a report on the reconstruction of Wilhelmshaven. At the same time, City Planning Counselor Otto Lehn organized the 1948 ideas competition. Kurt Brüning from the Lower Saxony Office for Regional Planning and Statistics, had commissioned the former regional planner of LOB Wilhelm Wortmann with the expert report, together with the former member of the 122 Speer task force, Max Karl Schwarz. The report was to provide the basis for the post-war land use plan. The continued employment of the planners of the "III Reich" and the Speer task force was practiced everywhere in the cities and proves that the "zero hour" did not take place.

In the report, Wortmann recommended that Wilhelmshaven should be built up towards the inland interior, as it had been during his time as NS state planner.[…]

The building regulations issued by the city of Wilhelmshaven in 1952 were issued, among other things, on the basis of § 2 of the regulation on building design of November 10, 1936. […]

The first larger reconstructions were based on the still existing drafts and plans of Bork, Schemm, zu Putlitz, Lübbers etc. There was no discussion of the architecture of the "III Reich".
_{— Ingo Sommer: "Die Stadt der 500 000. NS-Stadtplanung und Architektur in Wilhelmshaven", Springer Vieweg: Brauschweig, Wiesbaden, 1993.}

To emphasise this once again:

Although reconstruction did not really get underway until a few years after the war, it began before the end of the war.

The important turning point for urban planning in Germany was thus not the end of the war, but the bombing which had already produced grave effects on the cities by 1942/3. This period of time between the first planning measures and the actual start of reconstruction was from 1942/3 to 1949/50. It can be characterized as ‘Dreams in the Midst of Debris’, dreamt by urban planners and housing experts. Joseph Goebbels noted in his diary on 27 September 1944:

‘The Führer is convinced that although the enemy terror from the air is awful at the moment, especially for our medieval towns, it also holds a positive element in that it opens up these cities for modern transportation.’

This cynical optimism dominated the thinking of architects, urban planners and housing experts as well. They greeted the bombs as a great opportunity. Finally the stage was set for a radical new development of the cities. […] The guiding vision for planning at that time was that of the ‘orderly structured, low-density city’ – a vision that remained unchallenged from the 1930s through to the 1960s. This consensus was strengthened by the fact that many planners of this generation continued practising after the war. The profession was only minimally affected by de-nazification measures. As is pointed out by recent research, planning for urban reconstruction was in part influenced by the experience of planning Germanized cities in occupied Poland. It is also worth noting that certain terminology used in the reconstruction discussion was a continuation of the biological vocabulary of the Third Reich. So-called ‘organic urban design’, which had also found followers among the modern architects of the 1920s (for example Hans Scharoun), continually emphasized the analogy between city functions and the human body, for example transportation and the human cardiovascular system.

However, the ideas of the planning elite in the Third Reich which found their way into post-war planning were not fundamentally different from ideas about urban design in other European countries. The ‘Hamburg Generalbebauungsplan 1944’ for instance looked similar to the ‘Greater London plan’ of Abercrombie.
_{— Axel Schildt: "Urban Reconstruction and Urban Development in Germany after 1945", p141–161, in: Friedrich Lenger (Ed) : "Towards an Urban Nation. Germany since 1780", German Historical Perspectives/XVI, Berg: Oxford, New York, 2002.}

Especially noteworthy among those nazis that also were architects is the close collaborator of Albert Speer Rudolf Wolters. Tasked early with urban planning and reconstruction of destroyed by moral terror bombing cities he continued almost uninterrupted with this task after the war. What the nazis termed "Arbeitsstab für den Wiederaufbau bombenzerstörter Städte" (Task force for the reconstruction of bomb-damaged cities) continued after 1945:

Until the end of the war, the staff worked on the reconstruction plans; the individual planners were assigned one or more cities, for which they were to coordinate the reconstruction planning in cooperation with the respective urban planning offices. Shortly after the end of the war, the team split up and many members were assigned to reconstruction as department heads and advisory councils in the cities they had already supervised in the staff.

That means for Wolters to supervise the reconstruction of Coesfeld other Westphalian cities and numerous other building projects. He himself not only smuggled messages and goods to and from Speer out of war criminal prison cell. Wolters also coordinated immediately after the end of hostilities the re-integration of his dispersed group of nazis – until 1966. Wolters was a lifelong hardcore nazi out of inner conviction and consequently classified by the allies and post-war German society as "untainted, innocent". (André Deschan: "Im Schatten von Albert Speer", 2016.)

This group of nazi-planners includes names like Rudolf Wolters, Karl Berlitz, Friedrich Tamms, Helmut Hentrich, Konstanty Gutschow, Ernst Neufert, Friedrich Hetzelt, Reinhold Niemeyer, Herbert Rimpl, Karl Maria Hettlage, Hanns Dustmann, Wilhelm Hübotter.

For the specifics of how those ant-like parallel plannings came about:

There is no question that reconstruction planning after 1945 remained in the hands of the generation of planners who had gained definitive experience between 1933 and 1945.

Some of the non-nazi modernists had to leave Germany, leaving the nazis to themselves during the war. But those leaving were often staying away on greener pastures.

Prewar German colleagues inundated Gropius with letters beseeching him to throw his weight and prestige behind progressive planners and architects in their feuds with conservatives and holdovers from the Nazi regime. Hans Scharoun, Berlin's first postwar planner and an architect who had worked with Gropius arid Wagner on the Siemensstadt housing project in 1929, asked Gropius to join other progressive Berlin architects in protesting the rehabilitation in Baden-Wurttemberg of Paul Schmitthenner.

To such requests Gropius always responded that he considered himself an American […]

If there was any competition between tainted nazi visions and ideas less weighed down by what came before, then the result of fights for public opinion didn't turn out so well, as too much infratructure in terms of political personnel and appeals remained largely unharmed in place.

The polemics were, at least in part, an attempt to confront the legacy of Nazism. In 1948, Franz Rosenberg, then a member of the planning office of Braunschweig, asked Wagner to come to Germany instead of sending critical articles from America. "If you do this," Rosenberg wrote, "you will be doing something better than if you spend your time educating a generation of American students." Wagner replied:

Your invitation to come to Germany is truly tempting, and I would have long ago put this idea into action, had I truly believed that my time had come. It has not! Why? Because my chance, that is, your chance and the chance of the younger generation has not yet come. First the political twilight, by which Hitler seized the rudder, has to be cleared away. First the ministerial chairs and the chairs of the privy counsellors have to be shaken before it can be worth my while to invest the rest of my life in an action which is worth little more than starving. When my time calls me, then I will come, you can be sure of that.

The conditions for which Wagner hoped, of course, did not exist.

As the older generation of planners failed to assume the lead in reconstruction planning, that responsibility fell on the shoulders of those who had worked as planners under the Nazis.

And while the planning offices in most of the cities changed their top personnel after the war, the new officeholders could hardly claim spotless records. Indeed, it is remarkable that so many individuals who had been associated with wartime reconstruction planning found new positions as postwar planners. The most prominent included Rudolf Hillebrecht in Hannover, Heinrich Bartmann in Minister, Johannes Goderitz in Braunschweig, Helmut Hentrich and Hans Heuser in Krefeld, Friedrich Hetzelt in Oberhausen and Wuppertal, Hans Stephan and Walter Moest in Berlin, Rudolf Wolters in Coelsfeld, Werner Hebebrand in Frankfurt and Hamburg, Herbert Boehm in Frankfurt, Franz Rosenberg in Bremen, Friedrich Tamms and Julius Schulte-Frohlinde in Dusseldorf, Walter Hoss in Stuttgart, and Rudolf Schwarz in Cologne.

Since rebuilding bombed cities comprised the major planning problem during the war, they worked on reconstruction planning under the auspices of one Nazi agency or another, most likely the Arbeitsstab Wiederauf- bauplanung. Rightly or wrongly, they viewed their work as largely apolitical and technical and considered themselves members of an international movement that sought to cure the ills of urban life through planning. Strong critics of the unplanned metropolis, they nevertheless viewed great cities as the raw material for the exercise of their trade.

They considered the Nazi defeat and its replacement by a democratic form of government no obstacle whatsoever to continuing these planning activities. As apolitical technocrats, they considered their central planning concepts and models applicable anywhere—and everywhere. Consequently they went to work in a new location, either as an official planner or as an independent architect/planner, entering planning competitions or serving on competition juries. They maintained their wartime professional friendships but did not hesitate to cooperate with those who opposed Nazism ideologically. National professional associations provided them with forums for the exchange of ideas.

Viewing this generation of town planners as carriers of a set of ideas shaped by more or less common experiences underscores the extraordinarily pervasive continuities in planning.

And that is the gist of it:

The first 15 years after the war witnessed a very broad consensus on the fundamental goals of urban planning. Planners of all generations and all political backgrounds invoked the same concepts and vocabulary. The components of this consensus are familiar.[…]

The guiding concepts of postwar German planning clearly combined the second and third of Lynch's normative models: the mechanical and the or- ganic.[…]

Although Germany lacked a national reconstruction ministry, the process of urban reconstruction was at least in part organized nationally through a few influential private associations. In fact, at a meeting of the Arbeitsstab Wiederaufbauplanung in 1944, Karl Maria Hettlage had urged that centralized coordination and leadership of reconstruction be placed in the hands of the major private associations rather than in the hands of a government agency. Throughout the period of military occupation following the war, such associations helped compensate for the lack of a national government by providing a forum for the exchange of knowledge and experience. This exchange in turn helps account for some of the similarities in reconstruction that transcended local and state boundaries.

The natural home for these organizations would have been Berlin, the former capital. An Institute for Building was established by the German Academy of Sciences in the Soviet sector of Berlin (Institut fur Bauwesen an der Deutschen Akademie der Wissenschaften) in October 1947, with the architect Hans Scharoun as its head. With its 11 sections addressing such issues as housing, standardization, transportation, and historic preservation, the Institute for Building was conceived as a national institution, but the political situation in Berlin limited its activities primarily to that city. In 1950 it was transformed into the German Academy of Building (Deutsche Bauakademie) and put under a new director, Kurt Liebknecht, who ensured that the academy endorsed the Soviet approach to city planning and architecture. This alienated the western members, who subsequently abandoned the institute, leaving it without any influence in the West.

The organizational forms chosen for urban reconstruction were intended to make the process more efficient without being too authoritarian or bureaucratic. Though they differed in detail, the extraordinary organizational structures created alongside the normal building administrations were generally similar throughout Germany. The national, regional, and professional organizations kept planners, city officials, and architects aware of developments elsewhere. Experiences were shared through meetings and publications, and the successes of cities like Hannover were well known.

_{— Jeffry M. Diefendorf: "In the Wake of War. The Reconstruction of German Cities after World War II", Oxford University Press: New York Oxford, 1993.}

East Germany did have some mandatory guidelines in the form of The 16 Principles of Urban Design (german article)

There was no real nationwide plan, and it probably would have been of little use. Every city has its own local peculiarities, and each city had its own set of problems after the war. It would have been of little use to invest time and energy into a national plan when lots of time and lots of energy was needed at the local level to deal with the urgent problems of housing and infrastructure in the destroyed cities.

There were however some overarching trends in both East and West, e.g. towards wider roads and more green in reconstructed cities. In the West, modernist architecture was more popular immediately after the war, while the East saw more Stalinist architecture at that time.

Both East and West Germany have examples of cities whose inner-city layout was completely changed (e.g. Hanover in the West and Dresden in the East). Some cities in the West saw attempts to reconstruct some semblance of their pre-war layout (e.g. Nuremberg). East Germany had a permanent funding problem for larger building projects and Dresden even today has some downtown space that is basically unused (the parking lots south and east of the city hall).

Even if this is explicitely not part of the question, there actually was a national plan of this kind created during the Nazi era. This article (together with some Nazi quotes re. the advantages of German cities being reduced to ruins) argues that the people behind and the ideas formulated in that plan were very influential in post-war reconstruction, e.g. in the reconstruction of Hanover.

Short Answer:

No, with the exception of East Germany, city planning was done by a city and not by a State (Land) or national authority.

Between 1933 and 1945, with exceptions, this was also generally true.

Before 1933, cities generally delt with the city planning themselfs.

Depending on the period, general concepts existed about city development, which individual cities adapted to their needs.

Some of the ideas you meationed (parks, broad avenues, ring roads, bigger downtown train stations) existed and were implemented long before WWII.

Long Answer: sample Berlin

Until 1700, Berlin was solely a fortified city with a surrounding moat. Inside the city you had the typical windy streets and alleys with buildings being built to satisfy the needs of a geographicly restricted area.

Starting 1701, the city expanded mainly in the northern and western direction. Most of the broad streets/avenues created then still exist today. (Spandauer Vorstadt, Dorotheenstadt and Friedrichstadt).

Starting 1860, city planning was started for the, mainly country side, areas outside the (then existing) city boundaries.

Goal was to avoid known problems caused by the industrial revolution that happened elsewhere. One major problem that was addressed was the expected rural exodus, but due the underestimated amount of peaple arriving, this portion of the plan failed leading to a severe overcrowding between 1900 and 1930's. Mietskaserne were created, with around 5-6 floors (maximum hight fire department latters could reach), that had up to 6 backyards, each with at least 5,34 m × 5,34 m width (so that the fire department could turn around in). The last backyards were often small factories.

Other portions of the plan (Hobrecht-Plan) were successful in the area of street, sewage, parks and general transport. These areas were incorporated into the city on the 1920-10-01, when 'Greater Berlin' was formed.

After the fortifications and moats were removed, the moat area was used for inter city transport (railway, S-Bahn). As the outer tax wall was removed, it was replaced with ring-streets.

Around 1880 the city started to buy property within the former fortified area and then rebuild those areas based on the same concept as in the suburbs and outer areas. By 1910 many of the windy streets and alleys had been replaced, with sewage system extended to those areas.

Starting 1920, attempts were made to solve the overcrowding problem.

• Garden cities
• Bauhaus settlements

were created, togeather with green areas to better the general living conditions.

Starting 1945, many of the backyards of the Mietskaserne were not rebuild or completely replaced with new settlements, which was the fate of 'infamous' Meyers Hof:

• Ackerstraße 132 - Meyers Hof, 6 backyards

Starting 1960, in both parts of the city, high stories settlements (Märkisches Viertel, Gropiusstadt, Marzahn, Hellersdorf, Lichtenberg, Hohenschönhausen) were attempted that were similar in nature to self contained cities. In Berlin (West) this concept was, however, abandoned in the 1970's as being a to artificial environment (Retortensiedlungen, test-tube settlements).

Since then the goal is to improve existing living conditions with the retainment of existing social structures and avoiding social ghettos.

Railways

Originally, the railwys system developed in a similar mannor as those in Paris and London.

Between 1841 and 1875, 10 Head/Terminal stations (Kopfbahnhöfen), 3 of which had been abandoned by 1884:

• Dresdener Bahnhof
  • 1875-06-17 to 1882-10-15 (for passengers)
    • passenger trains rerouted to Anhalter Bahnhof
• Hamburger Bahnhof
  • 1846-10-15 to 1884-10-14
    • passenger trains rerouted to Lehrter Bahnhof
• Ostbahnhof (1867), also known as Küstriner Bahnhof
  • 1867-10-01 to 1882 (for passengers)
    • passenger trains rerouted to Schlesischer Bahnhof

Between December 1851 and July 1871 an overland connection railway connected the major head station with each other. This railway (passengers and freight) ran through tthe steets just outside the, then existing, tax wall.

Between 1867 and 1877 a Ringbahn was built, not only around the then city, but also around the suburbs planed in the Hobrecht-Plan.

Between 1875 and 1882 an East-West railway line (Stadtbahn) was built that connected 2 of the terminal stations (Schlesischer Bahnhof and Lehrter Bahnhof).

Decline of the Head/Terminal stations after 1945

• Anhalter Bahnhof
  • 1841-07-01 to 1952-05-18 (as train station)
• Görlitzer Bahnhof
  • 1866-09-13 to 1951-04-30 (passengers), 1987 (freight)
• Lehrter Bahnhof
  • 1868-07-11 (construction start) to 1951-08-28
• Nordbahnhof (Eberswalder Straße)
  • 1877-10-01 to 1985-07-11 (freight only)
• Potsdamer Bahnhof
• 1838-10-29 to 1945-02 (partially to 1946-07-27)
• Schlesischer Bahnhof (Ostbahnhof)
  • 1842-10-22, since 1882-02-07 part of Stadtbahn
• Stettiner Bahnhof (Nordbahnhof)
  • 1842-08-01 to 1952-05-18 (as train station)
    • passenger trains rerouted to Berlin-Lichtenberg

Hintergrund war, dass die DDR ab 1. Juni 1952 West-Berlinern den freien Zugang ihres Territoriums untersagt hatte.

Pilzkonzept, 1992

• Alt-Berlin – Wikipedia
• Hobrecht-Plan - Wikipedia
  • Rural flight - Wikipedia
  • Mietskaserne – Wikipedia (German only)
    • Meyers Hof – Wikipedia
• Bauhaus Orte in Berlin – Berlin.de
• Liste von Kopfbahnhöfen – Wikipedia (German only)
  • Anhalter Bahnhof – Wikipedia
  • Dresdener Bahnhof – Wikipedia
  • Görlitzer Bahnhof – Wikipedia
  • Hamburger Bahnhof– Wikipedia
  • Lehrter Bahnhof – Wikipedia
  • Nordbahnhof (Eberswalder Straße) – Wikipedia
  • Ostbahnhof (1867) (Küstriner Bahnhof) – Wikipedia
  • Potsdamer Bahnhof – Wikipedia
  • Schlesischer Bahnhof (Frankfurter Bahnhof, Ostbahnhof)
  • Stettiner Bahnhof (Nordbahnhof)
    • Bahnhof Berlin-Lichtenberg – Wikipedia
  • Berliner Verbindungsbahn – Wikipedia (German only)
• Berlin Ringbahn - Wikipedia
• Berlin Stadtbahn - Wikipedia
  • Geologische Karte der Stadt Berlin, im Maassstabe 1:15000, 1885
    • full resolution 7.342 × 8.406 Pixel
  • Potsdamer-Anhalter-Dresdner-Bahnhof, 1877
    • full resolution 7.517 × 4.976 Pixel
• Pilzkonzept, 1992