UNCIVIL ENGINEERING

Author: Oscar Bakker

Part 1 of the ‘Uncivil Engineering: U-boot Bunkers’ article was published in the previous edition of the ConcepTueel. This will be the second and last part about the U-boot bunkers. First, we start with a small recap; At the end of the previous article, we were at the end of the construction of the Keroman III bunker at the German naval base in the occupied French coastal town of Lorient. In the original plan, the Germans planned to build at least two more bunkers, collectively named Keroman IVa and IVb. However, the last of the planned Keroman IV bunkers were not completed. Only the foundation was finished after work ceased in April of 1944. By also using several smaller pre-war French bunkers, the Lorient submarine base could house a maximum of 30 U-boots at the same time.

During the war, the Lorient submarine base and the city itself were heavily bombed, especially in the spring and summer of 1943. The Allied bombers were unable to destroy the bunkers, even with the enormous Tallboy (12000 pound) and Grandslam (22000 pound) bombs. Therefore, they decided to cut off the base from their supplies by destroying the city itself: more than 500 highly explosive bombs and 60.000 tons of other ordnance were dropped on Lorient during the war, destroying more than 90% of the city itself. Many other towns with U-boot bunkers suffered a similar fate. However, the Allied air offensive never managed to destroy the Lorient submarine base itself. Only the Allied invasion of Normandy would put a stop to the Lorient submarine base: in August 1944, the last German U-boot here set sail for Norway. Other German U-boot bases in France suffered a similar fate. Often, these towns were designated as ‘Festungen”, fortress towns, to be held at all cost. As a result, most of these ports held out for months deep behind the actual frontlines. Often, U-boots were even chartered to secretly supply the garrisons of these besieged towns.

FIG. 1 U-boot bunker in Lorient | Photo: Jaenecke (2014)

FIG. 2 Section of Type 21 U-boot | Photo: Wikimedia Commons

Although the main German U-boot bases were situated in France, there were also U-boot bunkers in Germany and Norway. In Norway, U-boot bunkers were constructed in the port cities of Trondheim and Bergen, but U-boots were also stationed in other Norwegian places, depending on the deep fjords for their protection. Before the end of 1944, the main objective of the U-boots in Norway was to attack the Allied arctic convoys sailing towards the Soviet Union. After the Allied invasion of France, the importance of Norway grew as U-boots needed to be relocated to safe bases up north. As a result, the German planned a new wave of bunkers. However, these bunkers were never completed due to a lack of resources and time. Within Germany, a variety of U-boot bunkers was constructed in Bremen, Kiel, Helgoland and Hamburg. These bunkers were not only built for the purpose of housing and maintaining U-boots, but also for protecting the U-boot factories.

In the beginning of 1942, plans were made to build a U-boot bunker in Germany with enough space to house a central U-boot production shipyard. As a location, the Weser river in north-western Germany was chosen, close to the city of Bremen. This particular location was chosen carefully: the river would allow for relatively easy transportation of large U-boot parts from other production facilities all over Germany. Furthermore, the subsoil at this specific location was strong enough to carry the weight of the planned bunker, named Valentin.

Organisation Todt, the German organization tasked with the construction of projects of high strategic importance, began planning the construction of the Valentin U-boot bunker in late 1942 (Van Gorp, 2010). The bunker would cover a staggering surface area of 50.000 m2 . The construction began in the summer of 1943. In 1944, Organisation Todt had finished the foundation of the bunker. In the timespan of 18 months, most of the concrete walls, innovative prefab steel roof parts and other elements were installed. The bunker was deemed so important for the German war effort that workers and materials from other construction projects were diverted to the construction of the Valentin bunker. The Valentin bunker was divided in three functional workspaces: the workspace area, the transportation area and the U-boot assembly area. In the workspace area all the necessary equipment and arrangements for a production plant would be housed, such as storages, heating, energy supply, work spaces, administration, et cetera. The transportation area supported the transportation of workers and U-boot parts through the factory. The largest part of the bunker was reserved for the assembly area. The assembly area was planned to function as a giant assembly line. It was divided into 13 serried smaller spaces, where workers would connect all the U-boot parts from different factories in Germany. The assembly spaces were designed to be up to 18 meters in height, to enable to installation of the snorkels and periscopes. The total length of the bunker is 426 meters with a width of 70 to 90 meters (Figure 1). The thickness of the roof varies between the 4.5 and 7 meters, with the walls consisting of 4.5 meters thick concrete.

FIG. 3 Interior of Valentin bunker after bombings in 1945 | Photo: Imperial War Museum

In total, 8 large U-boot parts would be welded together in these assembly spaces (Figure 2). The plan was to produce a complete submarine every 56 hours. In the later stages of the Valentin bunker construction, the decision was made that the factory would be the final production line for the new Type 21 U-boot.

The Type 21 U-boot was a revolutionary new U-boot design. Where older U-boot designs could only spend a limited time under water at a very low speed, the streamlined Type 21 was designed to spend days under water while silently traveling at fast speeds. If it would have been designed and produced earlier, it could have made a significant impact on the war in the Atlantic.

However, the Valentin bunker was never fully completed. The construction was abandoned in the spring of 1945 when the bunker was almost 90 % ready. The most important reason for the fact that it was never finished was the frequent bombing raids made by the RAF, whose Tallboy and Grandslam ‘earthquake’ bombs managed to penetrate the weaker parts of the bunker roof (Figure 3) (Bircher, 2020).

In the end, despite the enormous effort of men and machine alike, the German U-Bootwaffe never managed to get a definitive stranglehold on Allied shipping. It was only for a short period in the spring of 1943, during a series of successful convoy battles in the mid-Atlantic, that the Germans managed to sink more Allied shipping tonnage than that the Allies could replaces in the same time span. Of the 40.000 men that served on U-boots, more than 30.000 men never made it home. A staggering number, especially in the knowledge that all U-bootmen were volunteers. Over 784 U-boots were lost out of the 863 U-boots that saw action. In turn, they sank 175 Allied warships and 2882 merchant ships. The U-boot war might not be the most well-known theatre of war by the general public, but the words of Winston Churchill: “The only thing that ever really frightened me during the war was the U-boot peril” say enough.

The attentive reader may have noticed that in this and the previous article the present tense is often used when describing the U-boot bunkers. This is for the simple reason that most U-boot bunkers are still standing today. These bunkers were so well built that it was simply impossible to remove them in a safe or cost-effective manner. Some of the bunkers were taken over by the navies of the occupied countries they were built in. The U-boot bunkers of Lorient for example served as base for the French

FIG. 4 Aerial picture of the Valentin bunker in Bremen | Photo: Olliku

(nuclear) submarine fleet till 1997, renaming the base to French civil engineer Jacques Stosskopf. He was an French maritime engineer who secretly gathered intelligence for the French resistance while officially working for the Germans at the Lorient bunker complex, an act of bravery that cost him his life.

Many bunkers today are either still in use as submarine bases, ammunition storages (as is the case with the Valentin bunker for the Bundesmarine (Figure 4)), museums or even as mooring places for pleasure yachts (Mortimer, 2019).

Bircher, E. (2020, January).

Deutsche U-Boote. Retrieved from Aus-der-Zeit: https:// www.aus-der-zeit.ch/books/derzweite-weltkrieg-band-07/page/ deutsche-u-boote Jaenecke, M. (2014). U-Boot-Bunker in Lorient. Potsdam: Fachbereich Bauingenieurwesen der

Fachhochschule Potsdam. Mortimer, G. (2019, November).

France’s U-Boat Bunkers Survived the War—And Thrive Today.

Retrieved from Historynet.com: https://www.historynet.com/ frances-u-boat-bunkers-survivedthe-war-and-thrive-today.htm Rogers, D. J. (2010). Overview of German U-Boat bases and bunkers 1941-1945. Van Gorp, S. (2010). Valentin: transformatie van een onvoltooide

U-boot montagebunker tot museaal gebouw. Eindhoven:

Eindhoven university of technology.