There is an extensive literature on German air defense efforts in World War II, though it is disjointed and has some noticeable gaps. Flak is amply documented, most notably the Westermann study. However, the aspect of Flak of most interest here, its fortified deployment, is not well covered in published accounts. I found ample documentation in archival records, especially the extensive collection of Luftwaffe manuals in Record Group 242 at the US National Archives and Records Administration (NARA II) in College Park, Maryland. Histories of the development of Luftwaffe air defense radar and the related issue of integrated air defense systems are not well represented in English except for the Svejgaard accounts on Denmark, though there are some useful German studies.
The Hampe study provides the classic account of German civil air defense during the war, but the focus is institutional and there is relatively little detail on the air-raid shelter programs. There is no historical overview of German air-raid shelter development, though the US Strategic Bombing Survey (USSBS) reports provide a useful start. Some of the individual city studies are especially helpful; the Hamburg study provides an excellent background into the overall civil air defense organization as well as shelter construction. There is a growing literature on the air defense infrastructure in various German cities, evidence of the recent upsurge in interest in Germany in local urban archaeology and the rise of the “Dark World” (Dunkle Welten) movement in Berlin of underground urban explorers. There are a number of German enthusiast groups studying the wartime shelters such as the Igel (Interessengemeinschaft zur Erforschung von Luftschutzbauten – see www.luftschutz-bunker.de). In addition, the recent rise in German interest in the experience of German civilians during the 1940–45 bombing campaigns has led to a broad range of published accounts which deal tangentially with air-raid protection.
The fortified factory program of 1944–45 has largely escaped any coherent study, though the programs are covered from a variety of angles in various histories. Some accounts of German jet fighter development deal with the associated underground factory program, and there are a handful of specialized studies on individual plants such as Valentin. The historical field of Holocaust studies has led to a great deal of research into the SS concentration camps, and the intimate connection between underground factory construction and the use of slave labour has uncovered a growing amount of information.
In August 1947, 338 Construction Squadron, Royal Engineers, set about preparing Gefechtstürm I of the Zoo Bunker complex for demolition. The first two detonations on August 30 and September 27, 1947 damaged the building, but failed to bring it down. A third attempt on July 30, 1948 finally collapsed the structure as seen here. The majority of the rubble was finally taken away in 1955–57, but the foundations were not removed until 1969. The hippopotamus enclosure of Berlin Zoo is now located on the site of the G-Türm. (NARA)
Aircraft Division Industry Report, (US Strategic Bombing Survey, Aircraft Division Report E-4: 1947)
Ausbildungsvorschrift für die Flakartillerie: Feldbefestigungen der Flakartillerie L.Dv.400/11a, (Luftwaffe: March 1940)
Ausbildungsvorschrift für die Flakartillerie: Stellungs- und Befestigungsbau der Flakartillerie L.Dv.400/11a, (Luftwaffe: October 1943)
Civilian Defense Division Final Report, (US Strategic Bombing Survey, Civilian Defense Division Report: 1947)
Cologne Field Report, (US Strategic Bombing Survey, Civilian Defense Division Report E-41: 1947)
Comparative Test of the Effectiveness of Large Bombs Against Reinforced Concrete Structures; Anglo-American Bomb Tests ‘Project Ruby’, (Air Proving Ground, Eglin AFB: 1946)
The Effects of Strategic Bombing on the German War Economy, (US Strategic Bombing Survey Overall Effects Division Report E-3: 1945)
The sturdy construction of the large air-raid bunkers has made their demolition prohibitively expensive. This example in the port city of Danzig (today Gdansk, Poland) was a fairly typical 1943 example, with a prominent air ventilation structure on the roof. It was built in the Old Town district near the harbour, currently at Ulica Olejarnia 2A. It was somewhat different from many other public shelters because it also housed a Luftwaffe command post, and had Flak guns mounted on the roof, a configuration generally frowned on elsewhere. (Wojciech Luczak)
Fire Raids on German Cities, (US Strategic Bombing Survey Physical Damage Division Report E-193: 1947)
Flak Defenses of Strategic Targets in Southern Germany, (AAF Evaluation Board-ETO: 1947)
The 14th Flak Division: Its history, organization, layout and role in the defense of central Germany, (CSDIC: 1945)
The German Flak Effort Throughout the War, (US Strategic Bombing Survey, Military Analysis Division Memo: 1947)
The German Passive Air Defense Services, (Historical Division, US Air Force: 1957)
German Underground Installations, (Joint Intelligence Objectives Agency: 1945)
Hamburg Field Report, (US Strategic Bombing Survey, Civilian Defense Division Report E-44: 1947)
Public Air Raid Shelters in Germany, (US Strategic Bombing Survey Physical Damage Division Report E-154: 1947)
Underground and Dispersal Plants in Greater Germany, (US Strategic Bombing Survey Oil Division Report E-112: 1947)
Underground Factories in Germany, (Combined Intelligence Objectives Sub-Committee: 1945)
Dietmar Arnold, Ingmar Arnold, Frieder Salm, Dunkle Welten: Bunker, Tunnel und Gewölbe unter Berlin, (Ch.Links: 2010)
Beck, Earl, Under the Bombs: The German Home Front 1942–45, (University Press of Kentucky, 1998)
Buggeln, Marc, Bunker Valentin, (Temmen, 2010)
Foedrowitz, Michael, Einmannbunker: Splitterschutzbauten und Brandwachenstände, (Motorbuch, 1998)
——, Luftschutztürme der Bauart Winkel in Deutschland 1936 bis heute, (Podzun-Pallas, 1998)
——, Luftschutztürme und ihre Bauarten 1934 bis heute, (Podzun-Pallas, 1998)
——, The Flak Towers in Berlin, Hamburg and Vienna 1940–1950, (Schiffer, 1998)
——, Bunkerwelten: Luftschutzanlagen in Norddeutschland, (Dörfler, 2006)
Gleichmann, Marcus, & Bock, Karl-Heinz, Düsenjäger über dem Walpersberg: Die Geschichte des unterirdischen Flugzeugwerekes REIMAHG bie Kahla/Thuringen, (Heinrich Jung, 2009)
Gückelhorn, Wolfgang, Die Koblenzer Luftschutzbunker im alliierten Bombenhagel, (Helios: 2008)
Golücke, Friedhelm, Schweinfurt und der strategische Luftkrieg 1943, (Schöningh, 1977)
Hampe, Erich, Der Zivile Luftschutz im Zweiten Weltkrieg, (Bernard & Graefe, 1963)
Immekus, Andreas, Militärische Anlagen in historischen Luftbildern: Flugabwehr, (Büro Immekus, 2009)
Koch, Adalbert, Die Geschichte der deutschen Flakartillerie 1935–1945, (Podzun-Pallas, 1954)
Kuffner, Alexander, Zeitreiseführer: Köln 1933–1945, (Helios, 2009)
Lemke, Berd, Luftschutz in Großbritannien und Deutschland 1923 bis 1939, (Oldenbourg, 2004)
Littlejohn, David, Defending the Reich, (Bender, 2007)
Lowe, Keith, Inferno: the Fiery Destruction of Hamburg 1943, (Scribner, 2007)
Maehler, Wilfred, Michale Ide, Luftschutz in Bochum, (Diguprint, 2004)
Moorhouse, Roger, Berlin at War, (Basic Books, 2010)
Müller, Werner, Die Geschütze, Ortungs- und Feuerleitgerte der schweren Flak, (Podzun-Palls, 1988)
——, Sound Locators, Fire Control Systems and Searchlights of the German Heavy Flak Units 1939–1945, (Schiffer, 1998)
——, Ground Radar Units of the Luftwaffe 1939–1945, (Schiffer, 1998)
——, The Heavy Flak Guns 1939–1945, (Schiffer, 1990)
O’Brien, Andreas, Holger Raddatz, Die verbunkerte Stadt: Luftschutzanlagen in Osnabrück un Umkreis, (Books on Demand, 2009)
Price, Alfred, Instruments of Darkness: The History of Electronic Warfare, (Scribners, 1967)
Purpus, Elke, & Sellen, Günther, Bunker in Köln, (Klartext, 2006)
Sakkers, Hans, Flaktürme, (Fortress Books, 1998)
Schiller, Peter, et. al., Die Bomber kamen bald jede Nacht: Luftschutz, Luftabwehr und Luftangriffe 1933/45 im Städedreieck Hamburg-Lübeck-Neumünster, (Arbeitkreis Geschichte im Amt Trave-Land, 2009)
Schmal, Helga, & Selke, Tobias, Bunker, Luftschutz und Luftschutzbau in Hamburg, (Christians, 2001)
Svejgaard, Michael, Der Luftnachrichten Dienst in Denmark 9 April 1940–5 May 1945, (Gyges, 2003)
——, The Kriegsmarine Command, Control and Reporting System, Bunkers and Electronic Systems in Denmark 9 April 1940–5 May 1945, (Gyges, 2007)
Thiel, Reinhold, Die Bremische Flugabwehr im Zweiten Weltkrieg, (Hauschild Bremen, 1995)
Titsch, Markus, Bunker im Wilhelmshaven, (Brune-Mettcker, 2005)
Westermann, Edward, Flak: German Anti-Aircraft Defenses 1941-1945, (Univeristy Press of Kansas, 2001)
Willen, Susanne, Der Kölner Architekt Hans Scuhhmacher: Sein Lebenswerk bis 1945, (Köln, 1996)