Nazi-era air raid shelters dot the landscape of Berlin – although they’re easy to miss. Most of these above-ground Bauklotzen have been transformed, woven into the city’s everyday urban fabric. Schöneberg’s four-story-high bunker on Pallasstraße became a post-war apartment complex. Berlin Story is a former bunker for the railway workers of Anhalter Bahnhof. Christian Boros houses his art collection inside the Reichbahnbunker Friedrichstraße (following its brief existence as a nightclub). One, however, remains true to its roots: a tall, proud centrepiece of a Gesundbrunnen park, still standing against all the odds.
The Humboldthain flak tower is arguably the most famous above-ground bunker in Berlin. Named so from shortening the German word Flugabwehrkanone (anti-aircraft gun) to Flak, it was one of three concrete monstrosities constructed in the heart of Berlin. Two were demolished after the war. Today, the only one left standing is a favourite viewpoint for locals and tourists alike. But how did Humboldthain’s flak tower come into being? Who used it during the war? And why did it almost disappear from Berlin forever?
Before the war
According to Holger Happel, author of Bunker in Berlin, the Nazi government wasted no time after assuming power to begin preparing for a racist war of aggression, including a coordinated air defence. Their priority was to correctly educate and train German civilians. Hermann Göring’s Aviation Ministry collected 13.5 million members of various small, private air defence cooperations under one umbrella organisation: the Reichsluftschutzbund. This provided fuel for Joseph Goebbel’s propaganda machine; a civilian air defence reinforced the idea that Germany could, at any moment, come under attack. German citizens needed to be mentally prepared and willing to justify any preemptive strikes against its neighbours.
At first, Berlin’s bunkers were limited to military personnel and essential workers, particularly railway staff. Planners sought to create cost-effective shelters. The advantages of above-ground bunkers were two-fold: not only were the costs limited, as construction was much faster, but direct hits were potentially preferable to those below ground. Above-ground explosions would dissipate in the open air, but hits on subterranean targets caused shockwaves that would travel through the earth and cause further damage. Still, despite all the Nazi Party’s talk of air defence, there was only space for about 4.5% of Berlin’s 4.2 million population in its air-raid shelters as World War II broke out.
The wake-up call
Everything changed on the night of August 25, 1940. Less than one year into the war, the unthinkable happened: at least 70 British fighter planes flew over the northern suburbs of Berlin, dropping bombs and shattering the illusion that the violence of the WWII only happened elsewhere. Hitler’s response to continued attacks from the RAF into September was the Führer-Sofortprogram. It sought to rapidly expand Germany’s civil air defence capabilities through the construction of thousands of bombproof concrete blockhouses.
The programme was about optics as well as particular material outcomes. The bunker-building plan would rapidly increase the number of refuges during air raids for German citizens (non-German citizens and concentration camp inmates, of which there were over 10 million at the peak of Nazi exploitation, were excluded). But it was also a show of strength, epitomised by the dual-purpose anti-aircraft guns emplaced upon the roofs of these shelters. These were added, at Hitler’s insistence, throughout the Third Reich (he even drew the first sketches of them), including significant ones in Vienna, Hamburg and Berlin.
Construction and wartime use
Over the following 18 months, a team of 3,200 workers erected three monstrous above-ground air raid shelters in Berlin: one in Volkspark Friedrichshain, one on the grounds of the zoo and one in Volkspark Humboldthain. Each consisted of two separate buildings. One was the flak tower, approximately 70m long, 70m deep and 42m high, with four giant 128mm flak cannons mounted on its corner turrets. The second was a control tower containing various meteorological and surveillance equipment for calculating in which exact direction the cannons were to fire their flak grenades. The flak grenades were literally ticking time bombs. Set to explode at particular coordinates and flight heights, they aimed to fatally damage a British or American aircraft by exploding into small pieces of shrapnel. In fact, this is where the expression ‘copping flak’ comes from – in other words, coming under fire.
In the aftermath of Humboldthain tower’s (partial) destruction, it became one of Berlin’s many rubble mountains that make up the highest points of elevation in the city.
Each flak tower had the capacity for a whopping 15,000 occupants during air raids, and each control tower could shelter 7,500. Civilians flocked to these structures. The 2.5m-thick walls and 3.8m-thick roof, the presence of anti-aircraft crews and the fact the towers had their own water supply, power systems, military hospital, internal heating and ventilation made them reassuring places to be. However, according to military historian and tour guide Matthew Mennecke, the difficulty of hitting high-altitude moving targets meant the flak grenades’ bark far exceeded their bite. The Humboldthain towers only shot down 32 aircraft over the course of the war. In fact, some claim that the flak grenades caused more damage to the city itself, when shrapnel fell from the sky, than to enemy planes.
They were far more effective during the Battle of Berlin in late April and early May 1945. Red Army forces essentially shuttled around the towers due to the fact the 128mm flak cannons had been converted into 128mm anti-tank cannons, which were both extremely precise and destructive against Soviet vehicles. For this reason, all three flak towers remained unconquered when the Berlin garrison officially surrendered in the early hours of May 2, 1945.
The post-war plan and the reality
As per the Potsdam Agreement, which set out the terms for demilitarising Germany after WWII all military infrastructure was to be destroyed. Berlin’s three towers lay in three different sectors, controlled by the French (Humboldthain), the British (Zoo) and the Soviets (Friedrichshain), and each administration employed their own methods to destroy their tower. According to Berliner Unterwelten, the Soviets destroyed the Friedrichshain tower in time for the first-year anniversary of the Battle of Berlin in 1946. The British needed three attempts to destroy the Zoo tower between 1947 and 1948. The French began the process in Humboldthain in 1948. The results? The compacted roof of the Friedrichshain tower is still visible in the Volkspark. The Zoo bunker was demolished and then completely removed by a specialist excavation team from Hamburg; the site is now home to the ‘World of Birds’, ‘Hippo Bay’ and ‘Rhinosaurus Pagoda’ enclosures. The Humboldthain tower was only half destroyed.
This begs the question: why was the northern façade of Humboldthain’s tower spared? The answer has to do, as it often does, with the Cold War. French engineers deliberately spared the northern façade because of fears that the demolition could impact the railway line that runs north of the tower. These train tracks were owned, operated and maintained by the Soviets. Any destruction of that line could spark Cold War tensions at a time when the relationship between the Soviets and the three Allied powers was rapidly deteriorating.
In the aftermath of Humboldthain tower’s (partial) destruction, it became one of Berlin’s many rubble mountains that make up the highest points of elevation in the city. Between 1948 and 1951, approximately 1.6 million cubic metres of debris was piled on top of the former flak tower, which was thereafter dubbed Humboldthöhe (Humboldt Hill) by the Bezirksamt Wedding. One year later, Volkspark Humboldthain officially reopened, with the former tower offering unparalleled views of a war-ravaged Berlin. The Sommerbad Humboldthain had already been constructed and opened a year earlier, turning Volkspark Humboldthain Park into a space of leisure and recuperation within the city.
History from the ground up
In the following decades, the rubble mountain disappeared, seeming like any old regular hill as vegetation began to grow over it. The interior of the flak tower was still, at least in theory, accessible for anybody who was adventurous enough to climb inside. However, the mass of wrought reinforced concrete covered in tonnes of rubble made it wildly unsafe. Indeed, in March 1982, Reinhardt Becker broke into the flak tower through a gap in the outer wall, only to plunge to his death down a shaft where a five-storey stairwell used to be.
One year later, Volkspark Humboldthain officially reopened, with the former tower offering unparalleled views of the war-ravaged city.
It was in the mid-1990s that a group of young people founded Berliner Unterwelten, with the aim of exploring Berlin’s historical underground infrastructure and making it more accessible to the public. Between 2001 and 2003, members put in over 8,000 hours of voluntary work to clear out and stabilise the interior and exterior of the flak tower at Humboldthain. In April 2004, they began offering public tours. Over the last 22 years, more spaces have been cleared out and stabilised, allowing Unterwelten to offer tours right into the basement of the building, which according to their spokesperson, Sascha Keil, are incredibly popular. It’s a powerful example of civil society intervention and voluntary engagement with the past, the bedrock upon which Vergangenheitsbewältigung – coming to terms with the Nazi past – is built upon.
As they cleared out the building, members of Unterwelten discovered an interesting surprise: nature had found its way into the core of the building. These days, the only creatures that seek shelter within the dark chasms of the flak tower are bats – hundreds of them. Inside tours therefore don’t take place between November and March, allowing the local bat population to quietly enjoy their hibernation. So, that’s what becomes of a tower made for war during peacetime. It becomes a strong and still presence around which Berlin continues to change; vegetation grows over it, animals sleep inside of it and people climb to the top for a beautiful view of the city it once played a role in destroying.
Visit the Flakturm at Volkspark Humboldthain. For guided tours see berliner-unterwelten.de
