World War II Database

Contributor: Hugh Martyr

The problems of the malfunctioning German Torpedoes in early WWII.

One of the lesser known reasons for the Allies winning the Battle of the Atlantic is what became known to the Germans as "Die Torpedokrise" or "Torpedo crisis" during the first year or so of the war. It was the time when the German U-boat (submarine) arm experienced technical malfunctions with the torpedoes. The time this problem took to resolve proved to be a break in which the Allies managed to improve their anti-submarine measures. By the time the Kriegsmarine (German Navy) finally succeeded in eradicating the problems Allied technology had advanced significantly and it was the Germans that were always having to catch up.

One of the first times that malfunctions were recorded was when, on 14 Oct 1939, Günther Prien, commanding U-47, had his epic venture into Scapa Flow in Scotland United Kingdom to sink the battleship HMS Royal Oak. Such was the success of this attack that the fact that Prien had had all the first four bow torpedoes fail and then had the stern torpedo also fail, went un-noticed. Despite being recorded in his war log nothing much was done to find out what had gone wrong. It had taken seven torpedoes at short range, at a large stationary ship, to finally get one to detonate. All of Prien's tactical skill and expertise as a commander almost counted for absolutely nothing, and the success of his astonishing achievement rested entirely on the fact that one of his torpedoes, the seventh fired, finally worked and the attack was a success.

Over the next twelve months the behaviour of torpedoes proved to be inconsistent, some failing to detonate and other just not hitting the target. The submarine commanders made constant complaints and Admiral Karl Dönitz, head of the U-boat arm, was assured that there was nothing wrong with the design and that the problem was with inexperienced and over-eager commanders. However, another highly proficient commander, Wilhelm Zahn had three torpedoes hit the battleship HMS Nelson and fail to explode. At the start of 1940 it was reckoned that 25% to 30% of torpedoes were failing. After meeting with Dönitz, Grand Admiral Erich Raeder sacked the Torpedo Directorate chief Oskar Wehr together with some of his scientific staff and appointed Rear Admiral Oskar Kummetz as the new chief. After merely a week on the job, Kummetz telephoned Dönitz and reported that he had proved beyond doubt that the torpedoes were defective in several ways. Discovering the problem was only the first step. There remained the task of correcting these defects. The winter of 1939-1940 was the coldest in forty years and thick ice in the Baltic Sea prevented any further tests and development. In fact, the problem of faulty torpedoes would not be fully solved until Dec 1942.

At the outbreak of the European War in Sep 1939, the German Kriegsmarine possessed two standard types of torpedo. A steam powered one known as G7a and an electrically powered one known as G7e. The G7a displaced 3,369 pounds dead weight whilst the G7e was a little heavier, displacing 3,534 pounds. At 23.5 feet long and 21 inches in diameter both looked identical and carried the same weight of warhead. The detonation of the warhead was the same in both types being an ignition device known as the "Pistol". The only difference in the torpedoes was the propulsion system: the G7a was propelled by a gas steam engine whilst the G7e had an electric motor driven by batteries. The gas-powered torpedo had the disadvantage of leaving a trail of bubbles as it ran through the water: as this wake was quite visible, the weapon was used more in evening or long-range attacks. The electric motors of the G7e made this type slower through the water and due to the batteries, the range was shorter. The running depth of the torpedo was governed by a depth-keeping system known as the Tiefenapparat.

Germany had a large stock of torpedoes left over from the First War, the Treaty of Versailles forbade the making and development of new torpedoes but said nothing about the stocks left over which consisted of the two types described above. The weapons were simply improved in their power units and detonation technicalities, making them faster and the war heads more powerful.

The problems that Oskar Kummetz found were threefold: the contact detonator, the magnetic detonator and the depth keeping ability all proved to be defective. The contact detonator used during the First World War was of a simple and reliable design. This detonator had been redesigned in the interwar years so as to transfer the impact of the blow back through a series of levers and give an impact angle of 69 degrees to perpendicular. Yet this design was found to have only been tested twice and then had had mixed results. The immediate remedy employed by the Germans was to replace the detonators with a copied version of the British torpedo detonator. This was made possible by the capture of HMS Seal in Apr 1940.

The magnetic detonator was supposed to fire when the torpedo passed underneath the target's keel, as it was triggered by the change in the magnetic field. This was failing due to the Allies reducing the magnetic field of their ships by degaussing. This on top of the fact that the earth's magnetic field varied as one travelled north and iron deposits beneath the sea bed could vary, meant that the whole magnetic detonating system needed to be re-designed and a new model was made available in Dec 1942.

However, with both these detonating systems working, the depth control was not functioning correctly, and many torpedoes were running two or three metres too deep or becoming surface runners.

At first the torpedo Directorate stubbornly refused to admit that this was the case. They tested many torpedoes in the Baltic and the great majority ran true to depth. The problem here lay in the fact that the torpedo trials and testing methods suffered two huge problems. Firstly, conditions during the trial shooting was completely different from combat conditions when the U-boat may have spent long periods submerged and secondly, live firing was strictly forbidden during trials. When new eyes looked at the trial data this problem was discovered. When a submarine was in action it would surface, submerge and dive deep many times, to maintain a healthy atmosphere within the boat compressed air was released, this then changed the atmospheric pressure inside the boat, air would be forced into the torpedo chamber effectively re-calibrating the depth sensor mechanism. The fired torpedo would then drive deep to maintain that pressure and pass harmlessly under the target. The problem could be solved by the U-boat crew adjusting the depth sensor before launch.

The problems were eventually found and rectified but by then there were new and effective anti-submarine measures that the Allies had developed, and in Jul 1942 the Allies were able to build new ships faster than the U-boats could sink them.

As a result of the torpedo crisis, several top officials of the Torpedo Directorate were court martialled for negligence in duties. Dönitz would write in his memoirs: "For the lessons one fails to learn during peacetime, one pays a high price in war".

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1.  Alan Chanter says:
28 Jan 2019 02:46:38 AM

A very interesting article. Thank you very much.