German U-Boat

The origin of the first U-boat bunkers traced back to the period of the First World War, where it was hardly a bunker at all. Along with the submarine, the First World War saw the introduction of yet another dominant weapon in the battlefield – the airplane. Whereas previously, ocean going vessels were threatened only by other vessels, but the introduction of the airplane brought about a new threat from the sky. Not only were airplanes reconnoitering the seas, but they were also looking for among other things, surface ships and submarines to attack. It soon became obvious that ships and submarines berthed in their moorings were sitting ducks and frequently became targets of attack.

The first protective structures for U-boats were not designed to protect against aerial bombs, but rather to conceal the presence of an underlying boat from prying eyes. The first such structure was erected in Brugge (Belgium) where sheet metal measuring 70 meters by 20 meters were laid out overhanging the mooring points. These were later reinforced by wooden beams, planks and earth, which provided little protection except from splinter explosions. Eventually, the coverings were reinforced by concrete and by now these shelters provided adequate protection against light bombs. The first shelter could accommodate five U-boats.

U-136 sails into its pen in Lorient. Safely berthed inside, these bunkers provided protection from air raids.

However, these structures were considered makeshift but as the threat from the skies grew in intensity, along with the size of the bombs being dropped, so was the need for a more permanent bomb resistant structure. From the early months of the First World War, the size of the air dropped bomb had grown from a mere 5kg to 700kg towards the end of the conflict. In response to this, the first bomb resistant bunker with concrete roofing was built, also at Brugge. It had eight compartments, with each compartment measuring 62 meters long, 8.8 meters wide and 6 meters tall (internally). These very much resembled the U-boat bunkers of World War Two.

By the opening of the Second World War, plans for proper U-boat bunkers complete with protection for dockyard facilities were already laid out well in advance. The objective was not only to protect the boats from air attacks, but also to enable minor repairs to be carried out without interruption from air raids. However, with the fall of France and the occupation of Norway, new U-boat bases were made available which were much more strategically advantageous due to their proximity to the Atlantic. Construction priorities then shifted from bunkers in Germany to those in the occupied countries.

There were also plans for building complete bunkered shipyards, fully equipped and self-sufficient with dry docks for major repairs and construction, but there were always other more pressing or urgent needs that these never saw fruition. Plans for the construction of bunkers as far away as the Mediterranean and the Black Sea were also conceived, but these too never took place.

Two Type VIIs undergo refit in the massive U-boat pens in St. Nazaire, occupied France.

The protection offered by these bunkers were adequate throughout the early years of the war, until 1943 or 1944 when the Allies introduced the Tallboy and Grand Slam bunker buster bombs. These 12,000 and 22,000 lbs bombs scored numerous direct hits and several bunkers were penetrated. The response was to further reinforce these bunkers from between 3 – 7 meters to 7 – 10 meters, but up to the end of the war, these were never completed.

A bunker holed by a Grand Slam bunker buster bomb.	Grand Slam bunker buster bomb. The figure provides a good scale of the size of the 12,000 pound bomb.

U-Boat Bunkers

U-Boat Bunkers in Germany, 1939 - 1941
Location	Name	Size (m)	Roof Thickness	No. of Docks	Capacity	When Constructed
Hamburg	Elbe II	137 x 62	3	0 dry, 2 wet = 2	6 boats	Dec 1940 - 1941
Hamburg	Fink II	151 x 153	3.6	0 dry, 5 wet = 5	15 boats	Mar 1941 - 1944
Heligoland	Nordsee II	156 x 88	3	0 dry, 3 wet = 3	9 boats	Jan 1940 - Jun 1943
Kiel	Kilian	176 x 79	4.8	0 dry, 2 wet = 2	12 boats	Nov 1941 - Nov 1943
Kiel	Konrad	163 x 35	3.5	1 dry, 0 wet = 1	5 boats	Apr 1943 - Oct 1944
Bremen	Hornisse	362 x 68	4.5			Mar 1944 (incomplete)
Bremen	Valentin	450 x 100	7.3			Feb 1943 (incomplete)

U-Boat Bunkers in France, 1941 - 1944
Location	Name	Size (m)	Roof Thickness	No. of Docks	Capacity	When Constructed
Brest	-	192 x 333	6.2	10 dry, 5 wet = 15	20 boats	Jan 1941 - Jul 1942
Lorient	Dom	81 x 16	1.5	2 dry, 0 wet = 2	2 boats	Feb 1941 - May 1941
	Scorff	129 x 51	3.5	0 dry, 2 wet = 2	4 boats	Apr 1941 - Aug 1941
	Keroman I	403 x 146	3.5	5 dry, 0 wet = 5	5 boats	Mar 1941 - Sep 1941
	Keroman II	403 x 146	3.5	7 dry, 0 wet = 7	7 boats	May 1941 - dec 1941
	Keroman III	168 x 142	7.5	5 dry, 2 wet = 7	13 boats	Oct 1941 - Jul 1943
	Keroman IVa	160 x 130	7	4 dry, 1 wet = 5	24 boats	Jul 1943 (incomplete)
	Keroman IVb	95 x 150	7	3 dry, 0 wet = 3		(incomplete)
St. Nazaire	-	291 x 124	7	8 dry, 6 wet = 14	20 boats	Mar 1941 - Jan 1942
La Pallice	-	195 x 165	7.3	7 dry, 3 wet = 10	13 boats	Apr 1941 - Mar 1943
Bordeaux	-	232 x 160	5.6	7 dry, 4 wet = 11	15 boats	Sep 1941 - May 1943
Marseille	Martha	??? x 230	Unknown	Unknown = 13 total	20 boats	Jan 1943 (incomplete)

U-Boat Bunkers in Norway, 1941 - 1944
Location	Name	Size (m)	Roof Thickness	No. of Docks	Capacity	When Constructed
Bergen	Bruno	131 x 143	6	3 dry, 3 wet = 6	9 boats	Nov 1941 - Jul 1944
Trondheim	Dora I	153 x 105	3.5	3 dry, 2 wet = 5	7 boats	Apr 1941 - Jul 1943
	Dora II	167 x 102	3.5	2 dry, 2 wet = 4	6 boats	Jan 1942 (imcomplete)