Lorient: the den of wolves

Lorient: the den of wolves


After the French defeat Germany has a new opportunity to patrol better the Atlantic Ocean, in search of enemy ships and not, in order to prevent the flux of supplies, weaponry, equipments, raw material, oil and foods, which are sent from North America to help Great Britain.

The five bases on the Atlantic French coast, Brest, Lorient (Kéroman). Saint Nazaire, La Rochelle (La Pallice), Bordeaux, represent the “wolves’ lair”, which are ideal to patrol the north eastern Atlantic Ocean and to find a shelter when needed.

The “wolves” that leave in search of prey are the notorious U-boats1, the most feared ships of the Nazi Germany.

The tactic adopted, ordered by their commander in chief, the Kommodore Karl Dönitz, is known as Rudeltaktik, the “tactic of the wolf pack”

We will see below the still existing facilities in one of the bases, the main one, more than 70 years after the end of the war and examine the most important facts related to the base of Lorient, with a few words to the scientific discoveries and the resulting technologies that had an important part in the Second World War.


The war between Germany and France ends with the defeat of the latter in June 1940. The north of the country and part of the Atlantic coast are occupied militarily by Germany, while the rest of France passes under the administration of a French government, based in Vichy, led by Marshal Pétain2.

The Kriegsmarine takes advantage of the availability of the Atlantic coast to undertake swiftly the construction of bases for submarines: the first inspection to identify future bases is carried out on June 23, 1940, just a day after the armistice was signed, and works begin in 19413, assigned to the Todt Organization4, and will continue until 1944, when they will be suspended for lack of material and men.

After the defeat of Germany and the liberation of France, bases will go back in the availability of the French, who used some for their Navy.

The Kéroman base

On June 28, 1940 it is decided to build the main base of the U-boats in the Kéroman peninsula, commandeering an area of ​​20 hectares5, destined to host the 2nd and the 10th flotilla of submarines. A few months after the first U-Boots start going to the base for supplies and general maintenance, carried out by German workers coming from the base of Wilhelmshaven, which has the biggest German port overlooking the North Sea. At the end of August ’40 the base is attacked by British bombers, for which it is necessary to build reinforced concrete shelters, with a roof of 3.5 m, able to withstand the most powerful bombs known at the time. On January ’41, the Todt Organization began the construction of two Dom-Bunker (also called Bunker-Cathedral, with very sloping walls to mitigate the direct impact of small air bombs), each capable to give shelter to a submarine type II (250 t), served by the existing slipway of the fishing port6. Over 15,000 people (who come to be about 25,000 considering the workers engaged in the construction of the airfield), housed in well camouflaged huts in a radius of 15 km around Kéroman, work in hazardous conditions in the construction of the enormous base7, 24h / 24 with work shifts of 12h. At night they work with artificial light, except when the base is under air attack8. Three gigantic blocks of concrete, cement and granite, called K1, K2 and K3, are built between February 1941 and January 19439.

At Kéroman II is also built a bomb-proof barrack, equipped with air conditioning, heating and ventilation, which can accommodate 1,000 men of the arsenal staff. Canteens, a galley, locker rooms and a cinema complete the facilities10.

Kéroman III, which is the largest block of all, in 1944 is equipped with a double roof, where the lower one is constituted by 3.5 meters of reinforced concrete and the upper one, which is 3 meters from the bottom, by regularly spaced beams between them. This kind of construction (fangrost), developed at the end of 1943 to face the new and more powerful allied bombs, make the piercing bombs explode in the space between the two roofs, used as a combustion chamber rather than to penetrate the main bunker below. A 12,000 lb bomb (Tallboy) falls in fact on the roof without creating damage inside of the block.

In the bedrock of the base, between 12 and 17 m, are built air-raid shelters for a total length of 1,200 m, with several entrances and exits11.


Kéroman I

Kéroman II

Kéroman III

Date of construction

from February to September 1941

from May to December 1941

from October 1941 to January 1943


120 meters

120 meters

138 meters


85 meters

138 meters

170 meters


18 meters

18 meters

20,5 meters

Roof thickness

3,5 meters

3,5 meters

7,5 meters

Thickness of the walls13

4 meters

4 meters

4 meters


The KI includes five lockers closed by armored doors, the pen in the water of the slipway, and a reserved space for the lifting winch of the latter.

The KII has seven pens and a garage that houses the translation plate and the two tractors, instead of the Flore Museum.

Block KIII is not designed for the same purpose as the first two. With seven docks that can accommodate 13 submarines, this more classical construction is similar to those of other bases of the Atlantic Wall (Saint-Nazaire, Bordeaux …). The roof thickness, built following the pace of allied bomb tonnage evolution, varies from 7.5 to 9 m.

In 1943 the construction of the block IV begins; it is necessary to accommodate the larger submarines of Nazi fleet, the type XXI, higher than the predecessors and about 10 m longer than the type VII14. The construction continues slowly and is interrupted on April 1944, for lack of material and for the imminence of the landing of the Allies, the D-Day.

Today the side wall of the K4 project of the future station, delimiting the two rails of the railway K3, is still visible.

Totally it will be used more than one million cubic meters of concrete to build the largest ever built architectural unit in France during World War II15, able to accommodate and protect 25 submarines.

The K1 block is provided with slipway (inclined plane), still visible, which allows the extraction of the submarines from the water in about 35 minutes and their shelter into K1 or K2, protected from air bombardments, in a total time of 60 minutes. The slipway (here in a reconstruction of the base showing the K2 and K1 bunkers facing each other) was made necessary by the rocky terrain where was the basis, which effectively prevented the rapid construction of pens in the water. That’s the operation16 in five phases:

  1. The entry of the boat in the slipway: a trolley wedge-shaped, on which rests an iron cot, goes down to the base of the slipway channel on a 10% inclined plane. The doors of the breakwater are opened and the submarine enters the channel.

  2. The drying of the slipway: the doors of the breakwater are closed and the water is pumped out from the canal. The boat, lying on an iron cot, leaves the lower dock.

  3. The raising of the submarine: the set cot + boat goes up again back to the pier between the K1 and K2, where the cradle and the boat are separated from the trolley conveyor, and deposited on a movable plane.

  4. The lateral translation with a stop in front of the pen: the movable plane, with the submarine on, moves laterally on 8 rails, carried away by an electric locomotive, and it can carry submarines up to 77 meters in length.

  5. The longitudinal translation and the entry into the pen of K1 or K2: the boat enters the cell in which it is to be parked, moving longitudinally17.

Once in the bunkers, submarines become unassailable. The thickness of the roof (increasing over the years), from 3.5 meters to more than 7 meters, ensures adequate protection against the most powerful bombs dropped by the Allied Forces (Tallboy, 12,000 lb, and Grand Slam, 22,000 lb, known as “earthquake bomb”).

On August 6, 1944 a Tallboy bomb hits the roof of Kéroman III, causing only a slight flexion. A second bomb falls outside the bunker, damaging an underground route protected by a roof of 2 m of reinforced concrete. A small armored door at 250 m from the impact point sees the shutter system crumble18. As a matter of fact no bomb can hit the docks and cause significant damages to the German shipyards before the 1944-45 period19.

What is now a real city under concrete houses in the block K1 the construction of a power and thermal plant, and a tower where the crews of the submarines train to the emergency evacuation of the boats.

The K2 block has a protected transformer, a barrack for a thousand people and many rooms and storage tanks for supplies.

Finally, the K3 block is surrounded by warehouses reinforced at the ground side on three levels.

The three blocks are connected by a tunnel which supplies them with the fluids necessary for their activities, namely compressed air, diesel oil, sea water, drinking water, in addition to electricity.

Following the Normandy landing (D-Day) on June 6, 1944, the Allied Forces make their way toward Brittany, where they arrive on August 1st. General Fahrmbacher, commander of the fortified town of Lorient, gets the bridges that lead to the city mined and barricades himself with about 26,000 German soldiers in the bunkers of Kéroman and the surroundings. About 20,000 civilians are trapped in the so-called “Poche de Lorient“, which extends from the river “La Laïta” to “Quiberon” and incorporates the islands of Groix and Belle-Île.

The Allied Forces abstain to take hold of the fortress, because their primary concern is the liberation of Berlin, and just set up a blockade around the “poche”.

They will spend nine long months before the surrender of the Germans, which took place on May 7, 1945, in coincidence with the surrender of Nazi Germany.


An undersea boat is a boat designed to navigate essentially on the surface, where it reaches its maximum speed, but able to submerge and navigate, at a reduced speed and for a limited time, up to a maximum depth of about 230 meters (WWII). Anyhow, after about 36 hours it has to emerge to change the air20.

The submarine, however, often used incorrectly as being synonymous with undersea boat, is a boat designed to navigate primarily in immersion and, of course, also on the surface, where the maximum speed is lower.

The Unterseeboot, better known as U-Boot, is a German submarine that was invented, with the name of U-1, on December 16, 190621. Only the Class XXI U-Boot (from June 1944) and XXIII (from April 1944), built at the end of the war, are true submarines22, which, thanks to Schnorchel (installed in early August 1944 on existing submarines)23, may remain for a very long time under water24.

The largest type of U-Boot is the VIIC; with 65925 boats built (more than 50% of the entire fleet used during the Second World War), its form has represented the submarine for excellence, and it has been the undisputed star of the famous Wolfgang Petersen’s film, Das Boot.

It consists of a cylindrical pressure hull, surrounded by a second hull shaped as that of a destroyer. During the submerging, the water invades the space between the two hulls, thereby decreasing the pressure on the outer surface26.

Unlike the submarines of the Italian Allied Forces, the German ones have a high degree of standardization, which allows a crew to switch from one boat to another without problems27.

Some features of the U-Boot VIIC28:




Displacement (t) surfaced


the weight of the water displaced by the ship

Displacement (t) submerged


Length (m)


Width (m)


Draft (m)


the vertical distance between the waterline and the bottom of the hull

Propulsion: Diesel

2 x 1400 hp

Propulsion: electrical

2 x 375 hp

Capacità carburante

113 t

Speed (knots) surfaced


31,5 km/h



14,1 km/h

Immersion time


Range (NM)29



@ 12 knots in surface

@ 4 knots in immersion

Max depth (m)


Implosion at 220 m

Torpedo tubes (bow)


Torpedo tubes (stern)




Naval guns

1 x 8,8 cm + 1 x 2 cm

since 1944: 1×3,7 cm, 2x twins 2 cm



plus 4 officers

The reputation of the U-Boot is mainly due to the campaign of attacks on Allied convoys (US and Canada) supplying Great Britain engaged in a hard war against the Nazis, during the so-called Battle of the Atlantic (September 1939 – May 1945).

In about five years of war the Kriegsmarine sinks on the whole 23 million tons of enemy or neutral vessels30, with U-Boot in the forefront with 14 million tons31. But a considerable price is paid: almost all of the surface fleet is lost, along with a high percentage of submarines.

During World War II 115632 boats are produced and only few survive to the end of the hostilities, being destroyed in combat 76532,33,34 units, about 66%. An U-Boot out three is sunk during its first mission35.

Of the 39,000 men embarked on U-Boot, many of them just eighteen, only 7,000 will survive, about 18%36.

The last boat to leave the base of Lorient on September 5, 1944 is the U-155; this is the end of the base as the dock to repair the U-Boot37.

After the surrender of Germany, on May 8, 1945, only 156 U-Boot surrender to the Allied Forces, obeying the orders of Dönitz; other 228 are sunk by the same crews32,38. The figures above are still being reviewed by experts.

Life on board

A tube about 60 meters long, of which about 3039 available for the maneuver and the housing of the crew, uncomfortable, cluttered with equipment and torpedoes, stinking and unhealthy, saturated with humidity, noise, obstacles, stale air saturated with carbon dioxide, excessive heat or cold, where no intimacy is allowed, boredom and fear alternate, the food is often very bad as time passes from the departure, the lack of hygiene (therefore the color of the uniforms and undergarments is black40, the shower is a mirage, it is impossible to shave, and also for missions three months long it is impossible to wash oneself) and the guard duties are hard to bear. The smell of the bodies mixes with that of the latrines, of the stagnant water in the bilge, of the kitchen, of the ubiquitous mold, of the oil smoke and the cologne used by men to remove from the face the salt left by the splash of water during on-call shifts. The wet clothes, soaked with salt water, never dry.

The compartment reserved for torpedoes is initially flooded with hams, sausages, bread, potato sacks. Even one of the two latrines is filled with food at the departure, so in case of urgent necessity several “emergency” containers are used, from the tin to the bottles. They need to use every centimeter of available space to store the food. After a few weeks, the black bread goes moldy and only the inside is still edible! “The food has a distinctive taste,” says a submariner: “diesel with a certain musty taste”41.

Neurosis and claustrophobic attacks also undermine the health of the crew and the room always illuminated42, night and day, does not improve the situation. The bunks (overlapping in groups of six on each side) used for the rest are never empty: a man gets off from his bunk, another one gets up for his turn to rest. It is the so-called “warm bed”.

Not to mention the times when they are under attack, in the half darkness of combat lights, and only the skill and coolness of the commander (recognizable by the typical white floppy hat and whose age range from 20 years old, U-155, to 54 years old, UD-5)43 are able to calm and reassure the crew (sometimes subject to attacks of Blechkoller44, a neurosis from tin which leads to paranoid or violent behaviors)45.

This, in brief, is the life on board a submarine46.

The hunting tactics (Wolfsrudel)

It is the one typical of the wolves: as soon as a submarine, sailing usually on the routes of enemy ships, meets a rival convoy47, it sends a coded radio signal to the base of operations in France, where a unified command (BdU48) has other submarines converged to a certain point of the ocean, identified by specific coordinates49 known only to the “Kriegsmarine”. They have been warned via radio50 by coded communications through the Enigma machine. The “pack” so formed (about 12 U-Boot) sails towards the convoy and launches the attack, usually at night, sailing on the surface to avoid the deadly SONAR, often penetrating inside of the convoy to hit the merchant vessels loaded with goods intended for Great Britain.

This tactics, while it allows an effective and fruitful coordination of the submarine fleet, on the other hand exposes each submarine to the risk of being tracked down and sunk by the Allied Forces that, after a period of deep crisis, have developed effective countermeasures, including the “Huff-Duff“, a radio direction finder, installed on board of ships, which uses the transmissions between the submarines and the command base51. The Germans will never know this device, ascribing the localization of their U-boats to the radar.

The leader of the “pack” is a military man, who has already command experience of submarines since the First World War, Karl Dönitz.

Born in 1891 near Berlin, he joins the Imperial Navy in 1910 and as a cadet, in 1912, embarks on the cruiser Breslau. He continues his career in the Navy, embarking on the U-39 as an official observer. Then he goes to the UC-25 as commander and, in 1918, takes command of U-68, in the Mediterranean Sea.

For a technical failure he is forced to scuttle and falls into the hands of the Allied Forces, remaining prisoner in Great Britain until July 1919.

Dönitz is a firm believer in the submarine warfare to the merchant navy and with his few U-boats (42) takes its first notable successes, arriving to convince the skeptical Hitler, he admired maniacally, to strengthen the U-boat fleet.

After a “happy time” in which the “wolves” of Dönitz are always sinking more enemy or neutral ships, the Allied Forces counter-measures (Sonar52, Radar, the Enigma code breaking, control of the air space with greater autonomy aircrafts53, economic resources deployed by the USA, etc.) win by knocking out what was then still the most technologically advanced fleet in the world. Since 1943 the decline begins that will last until the end of the war.

In the last days of the war Dönitz was appointed by Hitler as his successor and President of the Reich. He treats the surrender with the Allied Forces and is arrested by the British on May 23, 1945.

Judged as a war criminal in the Nuremberg trial, he is sentenced to ten years in prison on the basis of the only charges remained: “Crimes against peace and war crimes”54.

Released in 1956, after serving his sentence entirely in Spandau prison in West Berlin, Dönitz retires in a small village in the north of the FRG, where he writes his memoirs, published in 1968. He dies in Hamburg on December 1980. His funeral is attended by many old foreign navy soldiers55.

The Enigma machine56,57

Enigma is a portable electromechanical machine, much like a standard typewriter, able to code and decode texts. Invented in 1918 by German engineer Arthur Scherbius, it was initially proposed on the market for use in the business world, but with little success.

Only the use by the German armed forces will decide its success: they will buy more than 30,000 specimens58. And while those supplied to the “Wehrmacht” use three interchangeable rotors (to choose among 5, marked with Roman numerals) and 6 cables (will be 1016, 10 million of billion, the possible combinations), those of the “Kriegsmarine” will be rapidly expanded, specifically for the U-Boot traffic, with the installation of a fourth rotor (the 4 rotors are chosen from a set of 8, bringing the possible combinations to 1,59 x 1020, 159 billion of billion)59,60, which will result in a period of blackout in the cryptographic services of the Allied Forces, concentrated in Europe at Bletchley Park, an estate at about 75 km north-west of London. At the end of the war the staff had been increased from the initial 200 units to about 7,000 men and women61: among them there are linguists, chess champions, crossword experts and even experts in papyrology. Then the head of the center, commander Alastair Denniston, realizes the need to recruit some mathematicians. Among all towers Alan Turing, a brilliant mathematician, philosopher, decoder, dreamer, one of the fathers of the new computer science and, unfortunately for those times, gay. A colleague called him a “genius always ready”62 for his willingness to discuss his own ideas with anyone.

Despite his decisive and irreplaceable contribution to the “war of the codes”, which certainly shortened the war by saving so many lives, also in the enemy field, in 1952 Turing, instead of being considered a hero, was accused of having a homosexual relationship and sentenced by a British court to choose between prison or a hormone treatment (chemical castration). Having chosen the latter not to end up in prison, the scientist suffered heavy physical ailments. The depression caused by the treatment soon led him to suicide, procured from an apple dipped in potassium cyanide. Only on the 24th of December 2013, Queen Elizabeth II bestowed a posthumous pardon for Alan Turing!63

After the war Bletchley Park remains an inaccessible secret, and all the men and women who worked there kept the secret. Almost all facilities and documents in the site were destroyed after the war. Only in 1974, after the publication of a book by F. W. Winterbotham “The Ultra Secret”, one can finally officially talk about Bletchley Park.

The ASDIC (sonar)

The ASDIC64, better known as “sonar“, is a localization equipment developed by the Royal Navy at the end of the First World War to fight the danger of submarines.

It consists of a transmitter-receiver of highly directional sound waves (one narrow horizontal cone65), placed in a metal dome under the ship: if a sound wave strikes against a submerged object, it is reflected and picked up by the receiver. By measuring the elapsed time66 between the transmission of the wave and the receiving of the echo one has a reliable estimate of the object distance. The payload is about 1500 meters.

At this point depth bombs are launched and they can seriously damage the submarine, sinking it or forcing it to emerge, at the disposal of the guns of the ships or of the bombs dropped by enemy planes.

The inglorious end of the U-1206

On April 14, 1945, just a few weeks before the end of the war, the U-Boot 1206 is sailing underwater, at about 200 feet (61 meters), off the eastern coast of Scotland. It is a submarine type VIIC, the most numerous variant of any ever built U-Boot. It is 67.1 meters long, 6.2 meters wide and can reach a maximum speed of 17.7 knots surfacing and 7.6 knots submerging. It can submerge up to 220 meters and is armed with four torpedoes in the bow, one in the stern and one naval 88 mm gun.

It is under the command of the “Kapitänleutnant” (Lieutenant) Karl-Adolf Schlitt67, class 1918. An urgent call of nature pushes the commander to use the ultra-technological (and at high pressure) boat toilet. In fact, unlike the enemy submarines, which empty the waste in a tank and then pour again them in the sea once emerged, the German ones use a different system: the feces are discharged into the water even when sailing in immersion, through a system of valves and of pressurized chambers which allow to overcome the external water pressure. The system developed by German engineers is so complicated that, in order to carry out the maneuver to discharge into the sea, you need to call a trained submariner!

But commander Schlitt makes a fatal mistake: he decides to do everything by himself, using the weighty instruction manual that explains word for word the correct sequence required to send in the sea what will become a “torpedo” of feces. The maneuver is difficult, the commander stops and calls for help. The technician comes to help, but probably, not knowing what steps have been already accomplished by Schlitt, he misses the right sequence and opens the mouth for the water entrance, which is mixed with organic waste.

For the depths of bad luck, the gigantic batteries needed to power the electric motors of the U-Boot are located in a compartment beneath the toilet. The brackish water reacts with the acid of the batteries and causes the leakage of chlorine gas, highly lethal. The situation is serious and the commander has to order the rapid emergence.

Sighted and attacked by British planes and patrols, the crew gets safety on inflatable boats, but not before having destroyed the code book, launched the ready torpedoes and destroyed the others, and finally triggered the scuttling of the boat68. Four crewmen perish, 46 save themselves.

The commander Schlitt will die on April 2009, shortly before the birthday of 91 years.

In May 2012, off the coast of Scotland, Jim Burke, member of the Buchan Divers69 team, finds what seems to be the U-Boot 1206 wreck70.



1 Unterseeboot, literally “undersea boat”

2 Marshal of France and French statesman (1856-1951). From the winner of the Great War to the reactionary leader of a France humiliated by the occupying German, Philippe Pétain leaves a picture full of contrasts. In the national memory, he embodies both the victory of 1918 and the shame of the summer of 1940 and the crimes of Vichy. In 1940 he signed an armistice with Germany and obtained full powers by the National Assembly met in Vichy, he imposed a fascist regime, strictly dependent on Hitler’s Germany.

4 The Todt Organization (OT), named after its founder, engineer Fritz Todt, Minister of Armaments and Munitions, was a military engineering company that first operated in Nazi Germany, and then in all the countries occupied by the Wehrmacht, employing almost entirely forced labour (up to 1.5 million men and boys). After Todt’s death, due to an air crash in 1942, the OT was directed until to Germany’s rendition by Architect Albert Speer.

6 Fahrmbacher,W. Souvenirs de la base (Keroman, 1940-1945), Le Faouet, Liv’Editions, 2012, page 42

7 Fahrmbacher,W. Souvenirs de la base (Keroman, 1940-1945), Le Faouet, Liv’Editions, 2012, pages 50, 54

8 Rogers,J.D. Overview of GERMAN U-BOAT BASES AND BUNKERS 1941 – 1945, Missouri University of Science and Technology

9 The work is under the responsibility of a French engineer from Alsace, who speaks fluent German: Jacques Stosskopf. With his authoritarian methods towards the manpower, he succeeds in gaining the confidence of the occupier. But the complaint against him by a member of the Alliance network subjected to torture by the Gestapo reveals the true face of Stosskopf, an active member of the Resistance, who informs the Allies of all the submersible movements. The engineer is deported to the concentration camp of Natzweiler-Struthof, Alsace, where he was killed by the Nazis on September 1, 1944, shortly before the arrival of the Allies. His name is given to Kéroman’s base after the war.

10 Fahrmbacher,W. Souvenirs de la base (Keroman, 1940-1945), Le Faouet, Liv’Editions, 2012, page 56

11 Fahrmbacher,W. Souvenirs de la base (Keroman, 1940-1945), Le Faouet, Liv’Editions, 2012, page 50

12 http://patrimoine.lorient.frLa Base de sous-marins – Dépliants de visite

13 Fahrmbacher,W. Souvenirs de la base (Keroman, 1940-1945), Le Faouet, Liv’Editions, 2012, page 152

14 Rössler,E. U-BOAT: i sommergibili tedeschi, tecnica ed evoluzione, La Spezia, Fratelli Melita Editori, 1993, pages 353, 360

15 http://patrimoine.lorient.frLa Base de sous-marins – Dépliants de visite

16 Hellwinkel,L. Hitler’s Gateway to the Atlantic: German Naval Bases in France 1940-1945, Barnsley S70 2AS, Seaforth Publishing, 2014, page 63

17 Fahrmbacher,W. Souvenirs de la base (Keroman, 1940-1945), Le Faouet, Liv’Editions, 2012, page 52

18 Fahrmbacher,W. Souvenirs de la base (Keroman, 1940-1945), Le Faouet, Liv’Editions, 2012, page 53

19 Weinberg,G.L. Il mondo in armi, Torino, UTET, 2007, page 416

20 Valzania,S. U-BOOT – Storie di uomini e di sommergibili nella seconda guerra mondiale, Milano, Oscar Mondadori, 2015, page 26

21 Rössler,E. U-BOAT: i sommergibili tedeschi, tecnica ed evoluzione, La Spezia, Fratelli Melita Editori, 1993, page 19

22 Rössler,E. U-BOAT: i sommergibili tedeschi, tecnica ed evoluzione, La Spezia, Fratelli Melita Editori, 1993, pages 208 and following

23 Fahrmbacher,W. Souvenirs de la base (Keroman, 1940-1945), Le Faouet, Liv’Editions, 2012, page 44

24 A submarine snorkel is a device which allows a submarine to operate submerged while still taking in air from above the surface. [ https://en.wikipedia.org/wiki/Submarine_snorkel ]

25 Valzania,S. U-BOOT – Storie di uomini e di sommergibili nella seconda guerra mondiale, Milano, Oscar Mondadori, 2015, page 69

26 Botting,D. The U-Boats, Alexandria, Va, Time-Life Books, 1979, page 33

27 De Giacomo,A. – Bianchi G. Il T.V. Antonio De Giacomo, Comandante del Smg. Torelli in Atlantico, Massa, Sarasota, 2015, page 95

28 Rössler,E. U-BOAT: i sommergibili tedeschi, tecnica ed evoluzione, La Spezia, Fratelli Melita Editori, 1993, page 335

34 962 units, according to Botting,D. The U-Boats, Alexandria, Va, Time-Life Books, 1979, page 6

35 Valzania,S. U-BOOT – Storie di uomini e di sommergibili nella seconda guerra mondiale, Milano, Oscar Mondadori, 2015, page 4

36 Fahrmbacher,W. Souvenirs de la base (Keroman, 1940-1945), Le Faouet, Liv’Editions, 2012, page 57

37 Fahrmbacher,W. Souvenirs de la base (Keroman, 1940-1945), Le Faouet, Liv’Editions, 2012, page 182

38 Liddell Hart,B.H. Storia militare della Seconda Guerra Mondiale, Milano, Mondadori, 1970, page 555

39 Valzania,S. U-BOOT – Storie di uomini e di sommergibili nella seconda guerra mondiale, Milano, Oscar Mondadori, 2015, page 74

40 It is the “bitch lingerie” quoted by Lothar-Günther Buchheim, recalling his trip on the U96 in 1941.

41 Botting,D. The U-Boats, Alexandria, Va, Time-Life Books, 1979, page 104

42 Botting,D. The U-Boats, Alexandria, Va, Time-Life Books, 1979, page 17

45 Botting,D. The U-Boats, Alexandria, Va, Time-Life Books, 1979, page 17

46 Bucchheim,L.-G. Le Styx [e-pub], Paris, France Loisirs, 2015

47 The B-Dienst (Beobachter-Dienst – Navy Radio Information Service) could read the British naval codes, especially those of the merchant navy; Dönitz was then in a position to follow the convoys from their constitution in the ports until the discharges of the surviving ships.

48 Befehlshaber der Unterseeboote (BdU) was the title of the supreme commander of the Kriegsmarine U-boat Arm

49 In the operating room of Dönitz at Kernevel, not far from the base of Kéroman, one of the walls is occupied by a huge Atlantic Ocean card, divided into square sections, distinguished by two reference letters. Each sector is divided into 9 smaller squares, identified by two digits.

50 The transmissions were made in Short Wave, which allowed to reach the submarines up to 10 meters underwater.

51 Weinberg,G.L. Il mondo in armi, Torino, UTET, 2007, page 405

52 To escape the sonar for a few minutes, the U-Boot used the Pillenwerfer. It has the shape of a can of 10 cm, full of calcium hydrate, able to generate in the water thousands of gas bubbles, recognized as a submersible by the sonar.

53 Among them the new B-24 Liberator, long range bomber with a radar system on board and a high load of bombs.

54 Davidson,E. Gli imputati di Norimberga, Roma, Newton Compton, 2016

55 Williamson,G. German Commanders of World War II (2): Waffen-SS, Luftwaffe and Navy, Oxford, Osprey Publishing Ltd., 2006, pages 25-27

56 An operating simulator can be downloaded here: https://sourceforge.net/projects/enigma-sim/

57 An online simulator is available here: http://enigmaco.de/enigma/enigma_en.html

58 Singh,S. Codici & Segreti, Milano, BUR Saggi, 2001, page 141

59 Singh,S. Codici & Segreti, Milano, BUR Saggi, 2001, page 160

60 The Germans increased the security of Enigma by transmitting an additional key, unique for each message, using the daily key of the 28-day code book, distributed to each unit holding the encryption machine.

61 Singh,S. Codici & Segreti, Milano, BUR Saggi, 2001, page 163

62 Singh,S. Codici & Segreti, Milano, BUR Saggi, 2001, page 178

65 Botting,D. The U-Boats, Alexandria, Va, Time-Life Books, 1979, pages 110-111

66 In the water the sound is transmitted to about 1500 m / s, about 4 times faster than in the air

68 Blair, C. Hitler’s U-Boat War: The Hunted 1942-45, New York, Modern Library, 2000