M1940 series minesweeper in 1941.
Early Wartime Surface Vessels
The pre-war ship construction plan was abandoned shortly after the war started; ships nearing completion were finished, others were scrapped, and there was no further significant development of large surface warships during the war years. All of the ships launched henceforth had been designed long before the start of the conflict, and the naval designers concentrated on building small surface boats capable of operating in coastal waters under air protection.
Some of the boats built during the war were created in quite astonishing circumstances. Probably one of the wildest projects was the construction, in Norway, of the Navy’s smallest minesweepers. These Zwerge (Dwarfs) were the brainchild of Kptlt. Hans Bartels, who commanded the minesweeper M1 at the start of the war. After taking part in the invasion of Norway, M1 developed mysterious engine trouble and was unable to return to Germany with the rest of the flotilla. By the time the fault had been traced and repaired, the other ships were too far away for her to catch up, so Bartels reported to the senior German naval commander, who was only too pleased to use M1’s services.
Bartels distinguished himself by carrying out several extraordinary feats: he managed to capture a destroyer, together with an entire torpedo-boat flotilla; and, later, he even captured an Allied convoy and took it into a German-held port. The men of M1 also ‘defended’ several small Norwegian ports from possible enemy attacks from the sea, by making mock mines – ingeniously devised by welding spikes onto empty petrol cans – and then mooring them in the harbour approaches. This charade was given an air of reality when the British laid a few mines of their own! Unfortunately for Bartels, these were rather inconveniently placed – right in the German shipping lanes. Undaunted, Bartels and M1, together with several modified fishing boats, tried to clear them. Three of the fishing boats were lost in quick succession making it quite clear that existing craft were unsuitable for sweeping mines in shallow fjord waters. It was apparent to Bartels that he needed an easily manoeuvrable craft with a shallow draught, capable of passing over the mines without detonating them. Such boats did not exist, so Bartels decided to build his own. While looking for suitable designs, he found a Norwegian fishing vessel with all the necessary requirements. Unfortunately, the engines (which were almost certainly purchased from Sweden) did not fit, until someone struck on the idea of turning the plans around and putting the propeller in the bows. It worked. The bows were flattened, a new point added at the stern and, in the end, everything fitted together quite well.
Twelve such Zwerge were constructed, and the Supreme Commander-in-Chief of the German Navy was invited to the commissioning ceremony – and to pay the necessary bills. But Grand Admiral Raeder did not take up this offer and, in the end, Bartels moved one of them to Berlin, moored it in the canal outside Naval Headquarters and Raeder inspected it there. Raeder took a dim view of Bartels’ independence, however, and promoted him to the rank of First Officer of the destroyer Z34, in the hope that he might re-learn some naval discipline. Later in the war, Bartels returned to his unorthodox way of life when he worked under the equally unconventional Admiral Hellmuth Heye in the Midget Weapons Unit.
Accounts of events at the start of the war tend to highlight the sinking of the aircraft carrier HMS Courageous; the sinking of the battleship HMS Royal Oak in Scapa Flow; the Battle of the River Plate, when the pocket battleship Admiral Graf Spee was scuttled; and the Norwegian Campaign of spring 1940. But these famous actions give a slightly false picture of the war, because the majority of German ships were not sent out to hunt British warships. The main burden of the fighting at sea was carried by small vessels, such as U-boats, destroyers, torpedo-boats and minesweepers, which conducted numerous successful mining operations in British sea lanes. Mines, especially the magnetic variety, were certainly the most important weapon in the German naval armoury during the winter of 1939/40.
The magnetic mine was not a German invention for Britain had developed it before the end of the First World War – although with little success. By 1939, the German Navy had perfected the weapon which Raeder, certain there would be no war with Britain until 1948 at the earliest, carefully locked away in a top-secret store. With this ace up their sleeve, the Germans sat back, convinced that the Royal Navy were unaware of the mine’s presence in Hitler’s arsenal. But, in the event, it was they who were caught out: for, when war broke out, the few existing models were still lying in cold storage and, until mass production of the magnetic type could be organized, the Navy had to make do with old percussion mines.
The German Naval Command was well aware that, once they realized magnetic mines were being used, the British would quickly find the means to neutralize their effect. To do this, it would be necessary to find out how the detonation system worked. After that it would be a simple matter of generating strong magnetic fields that would cause the mines to explode short of their target. The de-magnetizing of merchant ships would also be possible. In a way, the German Navy was helped by having so few magnetic mines: ordinary mines were cleared by minesweepers, after which the channel was declared open to merchant shipping, while magnetic mines were not cleared during such sweeps. They remained on the sea bed, only rising as the first large iron ship passed over. The German Navy took great care to deposit these mines in areas where they would have maximum effect and where they were not likely to be washed ashore. Ironically, it was an aircraft of the Luftwaffe that finally rendered this most deadly weapon ineffectual, by dropping one on the mud flats near Shoeburyness (Southend, Essex) late in November 1939. The pilot could not have chosen a better place for presenting this valuable trophy to the Royal Navy, for it landed in soft mud without damage and without the safety destruct mechanism for shallow water switched on and only a short distance from a fully-equipped military workshop. A British naval specialist, Lt.Cdr. J. G. D. Ouvry, simply walked out to it during the hours of darkness, took rubbings of the screw and nut heads, and then returned in daylight with specially made tools for opening the mine. He thus defused one of the war’s most valuable prizes.
The T2 model of the G7e went in service with German U-boat fleets in 1936. In stark contrast with the G7a steam-driven torpedo, the T2 left no visible stream of bubbles to alert ships that they were under attack, and was virtually silent; however, these were the T2’s only advantages over the G7a torpedo. In all other respects, the T2 was barely functional and performed marginal when compared to the G7a. Its range was much less than the G7a’s at only 3000 m, and it ran much slower at 30 knots (56 km/h).
Poor range and speed were not the T2’s only problems. Both of its detonators were flawed. The magnetic influence mechanism, designed to allow the torpedo to run under the keel of a ship and detonate, breaking the ship’s back, was inconsistent; often a T2 would detonate prematurely, or not at all. This led the BdU to order that all G7e/T2 torpedoes be fired only for contact detonation. However, the contact pistol of the T2 also malfunctioned; the British battleship HMS Nelson managed to survive almost certain destruction when three torpedoes from U-56 struck on her keel, two broke upon hitting and the other failed to explode. Captain Wilhelm Zahn of U-56 was so depressed by the evident futility of his efforts that he needed to be briefly relieved of duty by Admiral Karl Dönitz in order to compose himself, while the civilian Naval Ordnance Corps, responsible for torpedo development and maintenance, continued to insist the U-boat captains were somehow at fault. Estimates of the failure rate of T2 torpedoes for one reason or another range between 20% and 40%.
Nevertheless, the German Navy, after much prodding by German U-boat Command (BdU), invested resources into correcting the T2’s flaws. Gradually, it improved, and by the end of the Norwegian Campaign problems with the contact exploder and depth-keeping gear had been mostly solved, with significant strides made in improving the magnetic proximity feature. At the same time, the T2’s range was increased from 3000 m to 5000 m and eventually 7500 m. By that time, however, the T2 was already being phased out of production
THE TORPEDO CRISIS OF 1939/40
During the early days of the war, it was realized that U-boats could get close to British harbours and ships without being detected, and that they were usually only discovered when their torpedoes failed to explode at the target. When this happened, the ‘eels’ (German slang for torpedoes) either detonated early or passed underneath the target, blowing up harmlessly on the other side. This often resulted in serious consequences for the firer, because the old G7a torpedoes – which were still being used – left a noticeable wake of small bubbles as they passed through the water, thus pointing to the U-boat’s position. The ‘G’ was derived from an earlier name before the word ‘torpedo’ became widespread, and the Germans used the code name Geradelaufapparat (running in straight line apparatus). The ‘7’ refers to the length in metres and ‘a’ to it being the first variation of this type).
The G7a torpedo worked quite simply by compressed air helping to burn fuel in a four-cylinder combustion engine, which was fed with a mixture of fuel, hot air and steam. The later G7e torpedoes were fully electric, with batteries and motor. Although these did not leave a wake, they had the disadvantage of requiring much more maintenance and had to be withdrawn from the tubes for battery charging about once every three days. Their performance was also inferior to the ‘air’ type.
Initially, most of the torpedo failures were attributed to war nerves on the part of the U-boat crews. It was thought that the men acted too hastily and did not complete the firing procedure. But the facts pointed to quite a different reason: only about one-third of the total of torpedoes fired detonated on target. By the end of October 1939, Karl Dönitz, head of the U-boat arm, was certain the fault did not lie with his men. Indeed, he was constantly being inundated with complaints from his commanders, of which the following are but a few examples.
Kptlt. Herbert Schultze had come into port with U48 and reported that half of the ten torpedoes he had fired had been duds. Less than a week later, Kptlt. Wilhelm Zahn had had several battleships lined up in front of U56’s three tubes – it was a Type IIC U-boat – and had fired a salvo at HMS Rodney. The crew had heard the torpedoes strike her hull, but there had been no detonation. After stopping a merchant ship, Kptlt. Viktor Schütze decided to sink it with a torpedo, but found that four had to be fired from very close range before one detonated. Shortly afterwards, Kptlt. Herbert Sohler ‘flew off the handle’ at his debriefing, telling Dönitz that on three occasions he had managed to get within point-blank range of a convoy: each time, it was like shooting at a solid wall of ships, yet his torpedoes achieved nothing. All he heard were two premature explosions.
Stories like these abounded throughout 1939 and well into the following year before the reasons for the failures were discovered. The situation during the Norwegian Campaign of spring 1940 was appalling: out of a total of forty-eight U-boats, forty-two engaged the enemy, but over thirty of these attacks failed because the torpedoes did not work. At least twenty-five Allied warships were attacked but only one submarine was sunk.
However, the first two U-boats sunk by enemy action were lost as a result of premature explosions alerting the escorts. The first casualty, U39, commanded by Korvkpt. Gerhard Glattes, went down on 14 September 1939 after attacking the aircraft carrier HMS Ark Royal. U39’s torpedoes were of the old-fashioned compressed air variety that left a tell-tale wake. Escorts were alerted and some men in HMS Foxhound actually spotted the U-boat’s dark shadow beneath the surface of the water. Foxhound raced over to the spot and dropped several well placed depth charges. U27, commanded by Korvkpt. Hans Franz, was the second boat to go down. Again a salvo of three torpedoes detonated short of their target and two escorts, HMS Forester and HMS Fortune, darted over to the suspected position. And again, well placed depth charges brought the boat to the surface. Some of the crew managed to get out before it sank and, through letters sent back to Germany from prisoner-of-war camps, at least the details of U27’s fate reached Dönitz’s desk. (Such information was written in code and sent to close relatives, who had instructions to forward mail to the Naval High Command.)
During November 1939, Dönitz recorded in his diary: ‘The Torpedo Inspectorate has perpetrated a real blunder.’ Fortunately, Grand Admiral Raeder had reached the same conclusion and hastily appointed Professor E A Cornelius to find out what had gone wrong and to eliminate the fault. Cornelius had worked as torpedo specialist at Eckernförde before the war, and his knowledge in this field spanned some twenty years. However, it was not until about mid-1940 that the fault was run to earth and the sordid details were brought to light at a court martial.
There were three major faults which, to make matters more complex, did not affect every torpedo. Some of these problems were not recognized until the end of the war. This, understandably, clouded the problem, for as one fault was isolated and rectified another would crop up. The three major faults were:
1. Peacetime experiments had not accurately simulated the rigours of war. Torpedoes had simply been put on board a ship and, a few hours later, fired at a target – hardly an adequate test when one considers that under war conditions torpedoes were tossed about by rough seas for days, sometimes even weeks, before being used. This was especially detrimental to torpedoes used by submarines. Air pressure inside a submarine was most variable, and would usually increase slightly the longer the boat remained submerged. Torpedoes were expelled from the tubes by compressed air, which would then escape from the machinery into the interior of the boat. (A special free-running piston would be fitted behind the torpedo and, when the order to fire was given, compressed air would be released into the space behind the piston. This worked in a similar way to an air gun: the piston was pushed forward along the torpedo tube, pushing the torpedo in front of it. The piston would stop at the end of the tube and the compressed air was allowed to escape into the interior of the boat, thus preventing it from sending tell-tale bubbles to the surface.) Such increases in pressure affected the controls of the torpedoes and made them run erratically. The depth mechanism, especially, was affected.
2. The explosive could be detonated by two different methods, the necessary adjustment for whichever detonation was required having to be made before the torpedo was fired. This was no great problem because it could be carried out while the torpedo was in the tube, waiting to be fired. The commander had the choice of either exploding the torpedo on impact, using the so-called contact pistol, or the detonation could take place magnetically. By the latter method, the torpedo would swim deep under the target and blow up beneath it. This had far greater impact than a torpedo exploding at the side, for such an explosion could easily break a merchant ship in two. The problem with the magnetic detonator was that too little was known about the earth’s magnetic fields. This was especially evident during the Norwegian Campaign, where it was thought the proximity of the North Pole and the abundance of iron ore (magnetic magnetite) could affect the torpedo mechanism. After the Norwegian Campaign the torpedoes were mainly used with the contact pistol.
3. Torpedoes had a safety mechanism to prevent them from exploding too close to the firer. This device worked quite simply with the aid of a small propeller at the front of the torpedo. The propeller would spin around when the torpedo travelled through the water, and this turned a screw that pushed the two contacts of the detonator together so that, if activated, they could touch. This safety mechanism made it impossible for the torpedo to explode accidentally until it had travelled at least 300m (a little over 320 yards) through the water. The blades of this propeller also acted as a trigger for the contact pistol and this was where the major fault lay, for each blade was marginally shorter than the radius of the torpedo. As a result, the explosives were detonated when the torpedo hit a flat target, such as those used for practice or when the torpedo hit the side of a merchant ship with a deep draught; but it was also possible for the torpedo to hit a curved hull without the triggers being pushed back to activate the contact pistol. In those instances, the torpedo would bounce off, slide under the target and often carry on swimming. The contact pistol worked quite well against merchant ships, but the same problem cropped up in later years when U-boats started attacking small warships escorting convoys.
Experiments with new magnetic pistols had started in 1927, as a result of irregularities discovered during the First World War. These tests had been carried out using the very old G7v torpedoes, which were an earlier type to the G7a compressed air variety. The new pistol, consisting of a modified magnetic pistol, had been tested during the autumn of 1928 by firing torpedoes at an iron plate suspended in water. The torpedoes missed their target, and hit the framework instead, but the detonators went off, suggesting that the pistols were functioning.
At that time, there was no independent body for testing new torpedo developments, and all the work – designing, building, testing and evaluating – was carried out by the Torpedoversuchsanstalt (TVA). This arrangement was not changed until almost the end of the Spanish Civil War, when Admiral Raeder ordered the establishment of an independent testing command to find out why torpedoes used off the Spanish coast were not functioning properly. This body, called the Torpedoerprobungskommando (TEK), subsequently appeared, and was considered by many people to be in direct competition with the TVA. Consequently, there was considerable friction between the two.
The TEK carried out several tests, including firing torpedoes at the raised hull of the old sailing ship Niobe, and discovered several irregularities. But their findings were channelled back to the Supreme Naval Command through the TVA where some people were of the opinion that torpedoes were functioning perfectly and anyone could make them fail if they tried hard enough. Apparently, some of the test results were not passed on to the Supreme Naval Command, and it was not until after the war had started that one of the TVA’s junior officers took matters into his own hands and complained directly to the admiral about the nature of some of his duties. He felt he could no longer tolerate the irregularities in the administration. After this, Raeder dismissed several top officials and, in the summer of 1940 ordered a full inquiry – by which time the Norwegian Campaign was over.
At a court martial held later, it was revealed that the trouble had been caused by the TVA, which had been responsible for what was described as criminal negligence’. But, apparently, they were not solely to blame, for several of their engineers were turned down when they requested ships for torpedo-testing in rough weather. Unfortunately, they had received little support, and often had to make do with small boats not capable of going far out to sea.