As the date for initiating Operation Rheinübung drew nearer, the crew on board the Bismarck made the best use they could of the days that remained. Gdynia offered little entertainment, so Müllenheim-Rechberg usually went to nearby Sopot, where he could enjoy swimming in the sea and visit bars. Often his good friend, Lieutenant Jahreis, accompanied him on this short trip. Jahreis was Bavarian, a kind man and full of vitality, but his previous appointment as turbine engineer had just been taken over by Lieutenant Gerhard Junack. Jahreis had been transferred to command damage control, a change that had been a hard blow for him, as he was well acquainted with the turbines and had created a good relationship with his men.
During one of the trips to Sopot, Jahreis and Müllenheim-Rechberg stay far too long at the local bars and returned very late to their hotel. For some reason, neither of them woke up until the sun had already climbed high up in the sky. They realized that it was too late for them to reach Gdynia before the Bismarck weighed anchor for the daily exercise. After a swift journey to Gdynia their fears were confirmed: the last longboat to the Bismarck had already left the quay. Müllenheim-Rechberg and Jahreis persuaded the captain of a tug to take them to the battleship. When they reached the Bismarck, the first man they saw was Commander Hans Oels, the ship’s First Officer, waiting at the gunwale. Oels was responsible for all disciplinary matters on board and with his distance and reserved manners, he was not a popular person. The men called him ‘the loneliest man on board’.
Müllenheim-Rechberg and Jahreis had expected a dressing-down from Oels. However, he just looked at them in his reserved way and said: ‘The captain awaits you on the bridge.’
Expecting the worst, the two culprits reported to Lindemann, but he only smiled at them. ‘Well,’ he said. ‘Now you return to your duties.’154
While Lindemann, Lütjens and the naval staff thought through all the details pertaining to Operation Rheinübung, the Bismarck and her crew trained to become ready for action. On 28 April, the Bismarck was reported to be fully combat-ready and she had taken on stores sufficient for three months. The squadron still had to wait for the Prinz Eugen to be repaired following the damage caused by the mine detonation. On 13 May it was reported that the cruiser would be repaired and completed with stores on 16 May. Thus, the squadron tasked with Operation Rheinübung would be ready to sail on 17 May, or at the latest on 18 May.155
On 5 May, Hitler visited Gdynia. His intention was to study the Bismarck and Tirpitz, which were both anchored at Gdynia. Hitler was deeply interested in military technology and the two battleships had much to interest him. In the morning he boarded the tender Hela. The small vessel brought him to the Bismarck, which was moored further out in the harbour. Lütjens hosted the visitors and had commanded the crew on deck. A slightly pale Hitler paraded by, followed by Lütjens, Lindemann and the head of the armed forces staff, Field Marshal Keitel. A full tour of the battleship would take too long, so Hitler concentrated on what he found most interesting, in particular, the artillery. In the aft gunnery computer room, Lieutenant Cardinal demonstrated how the fire control system worked. Hitler as well as Keitel, who was a former artillery officer, seemed impressed by what they saw.156 The Bismarck was expected to be able to fire at targets about 30km away while travelling at a speed of 30 knots. The firing control systems on the German ships had improved even on those available during World War I, which had surprised the British with their speed and accuracy.
After Hitler had inspected this technology, he listened to a presentation by Lütjens, in which the experiences from Operation Berlin were reviewed. Lütjens looked forward to using the Bismarck in a similar way. With such a powerful warship, it was no longer imperative to avoid strongly escorted convoys. The main problem was to reach the Atlantic undetected.
‘Do not the superior numbers of the British Navy present a grave risk?’ Hitler asked.
‘The Bismarck is superior to any British battleship,’ Lütjens retorted. ‘Her firepower and protection is so outstanding that there is no need for fear.’ After a brief pause, he added that even after a successful break-out, there were disquieting factors, in particular British torpedo aircraft operating from carriers.157
Hitler was not familiar with naval warfare and was anxious about the loss of prestige suffered if a major German warship were sunk. The high-ranking German naval officers were well aware of this and it may have been the reason why Lütjens gave a rosy presentation of the forthcoming operation—despite the fact that he had misgivings. Lütjens carefully avoided giving any starting date for Operation Rheinübung, possibly because he wanted to avoid objections from Hitler. Perhaps Raeder’s absence was motivated by a fear that Hitler would ask him about forthcoming operations.
Lunch was served on board the Bismarck. It was well known that Hitler preferred vegetarian food and a vegetable stew was served. The meal was enjoyed without much conversation, but afterwards Hitler spoke about the German minority in Romania, which he considered to be persecuted by the government. If the persecution was not stopped, he intended to bring these people home to the German Reich. The issue was not the most urgent one for the German naval officers around Hitler in the mess, but when the Führer shifted topic to the role played by the United States, his audience grew more interested. Hitler did not believe the Americans would enter the war, but Lindemann disagreed. The conversation was ended with a short speech by Lütjens.158
After five hours on board the Bismarck, Hitler and his entourage left the battleship on the tender Hela, which brought them to the Tirpitz, where Captain Topp greeted them. He used the opportunity to express his wish that the Tirpitz might accompany the Bismarck during the forthcoming operation. Hitler let Lütjens and Raeder settle the issue. Neither of them agreed with Topp, as they regarded the crew of the Tirpitz as being insufficiently trained. As Hitler had already seen so much of the almost identical Bismarck, his visit on board the Tirpitz was briefer.159
The crew of the Bismarck used the remaining days to make every-thing ready for a long voyage on the Atlantic. The crew of the ship usually numbered 2,065 men but for the forthcoming operation, more officers, seamen and other officials were on board. Lütjens brought his staff, who were not included in the crew of the battleship.160 Beside Captain Harald Netzbandt, Lütjens’ chief of staff, there were many officers specialising in fields such as meteorology, communications, artillery, operations, surgery and personnel matters. In addition, there were liaison officers from the Air Force and submarine forces.161
Several war correspondents and photographers accompanied the Bismarck. They were supposed to film and write about the operations for propaganda purposes. Several prize crews had also arrived. Their task was to sail captured ships to German-controlled harbours.
The men in the so-called Beobachtungs-Dienstgruppen (hereafter B-Dienst), were experts in radio interception and deciphering. It was their task to monitor British wireless communications and break the codes. The British used a fairly simple code system, in which a combination of letters represented a phrase or a word. It was assumed that the receiver had a proper code book with which to decipher the message. Without the code book, the content of the message was incomprehensible.
The reality was a little different. The British had used the same system before the war and in a few instances, carelessness had resulted in messages being sent both coded and in plain language. By identifying these messages and comparing the deciphered version with the nondeciphered, the Germans gradually began to understand the British code. Then, by further comparing recently intercepted messages with those that had already been deciphered, the Germans could often work out their content.
Towards the end of 1940, the Germans could easily interpret at least half the messages sent by the Royal Navy.162 On 11 November the German surface raider Atlantis had captured the British merchantman Automedon, on which they found a code book used by the British merchant fleet. It provided the Germans with further clues on how to decode British wireless messages. This was especially useful after the British introduced changes to their codes during the autumn of 1940. Although the B-Dienst was not quite as successful at the beginning of 1941, their service might provide vital support when decisions were to be made by the German commanders during Operation Rheinübung.
It required substantial stores to feed the more than 2,000 men on board the Bismarck. The meat from 300 cattle and 500 pigs was taken on board and properly stored.163 Also, large amounts of potatoes, flour and vegetables were needed. Significant quantities of articles of consumption were loaded, such as cigarettes, which were rationed. It took several days of intense activity to make the ship ready to sail, and it was more or less impossible that this activity might go unnoticed by anyone who might want to pass that information on to the Allies. The most that could be hoped for was that unexpected delays would make it more difficult to guess when the ship was actually departing.
The squadron was finally ready to commence operations on 18 May. Although the Bismarck and Prinz Eugen attracted most of the attention, they were not the only ships that participated in Operation Rheinübung. As in previous operations, the Germans stationed several tankers and supply ships on the Atlantic. They were to sail from France or Germany in time to take up positions where few or no ships sailed regularly, from where they could provide the Bismarck and Prinz Eugen with fuel oil, but also ammunition and provisions. The tankers Heide and Weissenburg left Germany to take up positions in the Arctic Ocean and the tankers Belchen and Lothringen left ports in France to sail to predetermined positions south of Greenland. The tankers Esso Hamburg and Breme left France for positions north and south of the Azores. In addition, the supply ship Ermland set course for the area north of the Azores. Finally there were four weather observation ships and the tanker Wollin. The latter sailed for Bergen in Norway, where she would await Lütjens’ squadron if he decided to refuel at Bergen.164
Unlike previous operations, the Germans had decided to use special reconnaissance ships to assist Lütjens during Operation Rheinübung. They used fairly fast merchant ships which would take part in the search for convoys. This was as a result of Lütjens’ awareness of the valuable contribution that the tankers Uckermark and Ermland had made to Operation Berlin. They had ably assisted in searching for ships off the American coast during the final part of the operation. This time the Germans specially selected ships were detached from the very beginning, which reduced the risk of losing the valuable tankers. On 17 May the first ship, the Gonzenheim, left La Pallice near La Rochelle. The following day the Kota Penang left the same port. Both were instructed to await Lütjens’ squadron south of Greenland.165
While Lütjens’ squadron was making final preparations for sail, events were taking place elsewhere that were to have significant consequences for the war in the Atlantic. On 7 May, two days after Hitler’s visit to the Bismarck, the German submarine U-110 took part in attacks on a British convoy south of Greenland. The convoy was repeatedly attacked on several nights and five merchant ships were sunk. But on 9 May, depth charges from the corvette Aubrietia severely damaged U-110. The submarine was forced to the surface. In great haste, the submarine commander made a grave mistake. He ensured that the scuttling charges were properly primed before the last crewmen entered the life boats, but he forgot to throw the code books and the war diary over board. It turned out that the damage to the submarine was not as extensive as was originally believed and the charges never detonated. British seamen boarded U-110, where they found the code books for the German Hydra code, which was in widespread use by the Kriegsmarine in northern Europe.166
The Germans used a cryptography machine called Enigma. Without delving too deeply into its construction, it can nevertheless be said that it was advanced enough to lead the Germans to believe that their ciphers could not be broken. However, a branch of British intelligence, known as Ultra and located at Bletchley Park in Oxfordshire, had obtained an Enigma machine from the Polish in July 1939. Early on, the Polish intelligence had copied the Enigma machine and by 1933 they had already deciphered German radio traffic. When Poland fell to the German invasion in 1939, much of the valuable work performed by Polish intelligence had already been made available to the French and British.
The first code broken by Ultra was the so-called ‘red code,’ used by the Luftwaffe. Somewhat later, in April 1940, this was followed by the ‘yellow code,’ used by the German army. At the end of the month, the trawler Polaris was captured along with a copy of the German naval codes. For a few months the British were able to interpret German messages, until the German army changed its procedures and the code keys taken from the Polaris expired. The deciphering work became much more difficult, but in December 1940 the system used by the Abwehr (German military intelligence) was broken and towards the end of February 1941, the ‘light blue code,’ used by the Luftwaffe in the Mediterranean, was also broken.167
By spring 1941, Ultra could decipher Luftwaffe messages almost as quickly as the Germans, and although messages from German army units could still require weeks to break, many troop movements in the Mediterranean could be monitored, because the transportation services still used the older procedures. But there was a very important category of German signals that could not be broken by Ultra: the Hydra system used by the German Navy. At the time of Operation Rheinübung another system was about to be introduced in the Kriegsmarine, called Neptun, for use with the heavy warships. Messages coded with Hydra or Neptun could not be deciphered by Ultra. However, with the successful capture of U-110 this all changed.
The German code keys, call signals and the Enigma machine were transferred to the British destroyer Bulldog, and the submarine was taken in tow towards Iceland. However, the following day the U-110 sank and the disappointed British had to cut the rope and watch the submarine disappear. With hindsight, the British did not regret the loss of the German submarine, as they believed the Germans had agents in Iceland who would alert them to the news that one of their submarines had been captured. It might have provoked them to change at least the code keys. As it was, the Germans did not receive any information about the fate of U-110. Three days later, Lieutenant Allan Bacon, liaison between the Royal Navy and the British intelligence service, arrived in Iceland and examined the papers. He clearly realized the importance of the Bulldog’s haul and sent a brief telegram: ‘This is exactly what we have been looking for.’ As a precaution, the documents were photographed before being flown to London.168
The British were also fortunate in making another fine haul. On 7 May, they captured the weather ship München, complete with code keys for the entire month of June. As these ships remained at sea for long periods, the British realized that the code keys must remain valid for long periods. The capture of München was the result of a deliberate operation to catch one of the weather ships. These two events were a breakthrough for the British intelligence services. The U-110 was especially important, as the haul included a complete Enigma machine of the most recent type. With the Hydra code keys it was possible to follow the reports from German submarines, tankers, supply ships and weather ships during the forthcoming months. Furthermore, during this period, knowledge was gained which would improve the chances of breaking German codes once the current code keys had expired. Also, by studying how decrypted Hydra messages were structured, chances of breaking Neptun messages improved, although it could take between three and seven days to decipher a message from the big warships.
Still, from the German perspective the concept of waging successful cruiser warfare rested first and foremost on their ability to surprise the enemy. British acquisition of the codes meant that the required secrecy could no longer be depended upon, although for the moment the German Navy had no idea that their codes could be broken. When Lütjens attended to the final details for the planning of Operation Rheinübung, he had no inkling of how close the enemy was to gaining the initiative.