The G7e Torpedo

Hitler’s disdain for the British, which began with Britain’s intervention in the Great War and grew with each obstacle they put in his way, had led him to obsess over the Kriegmarine’s ability to thwart the Royal Navy’s power at sea. This had led to strict scrutiny of the German Navy’s forces, its arsenal in particular. Grasping the importance of U-Boats and their affect on British shipping during the Great War, Hitler focused a great amount of time on torpedo functionality.

The History of the German Torpedo

A U-boat was built for one purpose only – and that was to torpedo enemy ships. If it failed in this, then it failed in its mission. And the weapon of choice of U-boat commanders was the torpedo, for which there was no other alternative during a submerged attack.

Early German torpedoes were a combination of two worlds. They were both technologically sophisticated, and yet unreliable. During the Great War, standard U-boat torpedoes were driven by an alcohol fueled engine which possessed good characteristics of speed and range. The contact detonators used on these torpedoes were also of simple design, making them mechanically reliable. All the U-boat commander had to do was to calculate the right torpedo firing solution, and if he fired it right, then he could count on it to run true to its course.

However, two main drawbacks existed. First, the alcohol fuel engine left a telltale trail of bubbles on its way to its target. This could alert a watchful lookout and give the enemy time to perform evasive maneuvers. Second, the contact detonator, although mechanically reliable, was designed for the torpedo to explode on impact with the side of the ship. Often it would take more than one torpedo to sink its target, and if the opportunity did not present itself, then the ship often managed to limp back to port.

German scientists worked to improve their torpedoes, so that it would not leave a visible trail of bubbles and where it would take just one torpedo to sink a ship. The solution was a highly classified and sophisticated torpedo – the wakeless electrically powered G7e torpedo, armed with a completely new magnetic detonator. Even the Allies had no knowledge that the Germans had successfully developed a wakeless electrically powered torpedo. The new battery powered motor meant that no exhaust gases were expelled, and the magnetic detonator was designed to travel under the keel of a ship and then detonate. Such underbelly explosions could break a ship’s hull in two, sinking it with just one torpedo. Not only the propulsion system and firing mechanisms were new, in fact almost every part of the G7e torpedo was redesigned.

Under Hitler’s direct orders, the G7e was thoroughly tested to determine how useful this great new weapon would be. Fatal flaws were rapidly discovered. Reports of poor range and speed as well as early detonation and failure to detonate were frequent problems, resulting in a 250-40% failure rate of all torpedoes fired.

Enraged by this discovery, Hitler ordered the Torpedo Directorate chief Oskar Wehr sacked and greater attention placed on solving this critical problem.

Design flaws were quickly discovered. Often times, when a problem was discovered and corrected, other new problems were uncovered as a result of the fix. Problems fell into three main categories: contact detonator, magnetic detonator and depth keeping ability.

The detonator itself had been completely redesigned to transfer the impact of the blow backwards through a series of complicated levers. In theory, it was supposed to provide a wide impact angle of 69 degrees to perpendicular. However, in practice, this was closer to 40 degrees.

The magnetic detonator proved immune to simple fixes. It was supposed to detonate when it passed underneath a ship’s keel, as it was triggered by a sudden change in magnetic fields. This did not work as intended due to the earth’s magnetic fields varying at different geographical locations and influence by iron ore deposits beneath the sea bed. Only when the completely redesigned Pi2 detonator had been introduced in December 1937, was the problem of the magnetic detonator solved.

But even if the detonators had been working flawlessly, problems with depth keeping meant that torpedoes were running two to three meters too deep. The depth keeping device worked by using an atmospheric chamber which controlled running depth. The Torpedo Directorate conducted new tests and could not discover any flaws. This occurred because the test torpedoes were launched from normal atmospheric conditions. But since atmospheric pressure inside a U-boat varied greatly, especially after prolonged submerged activity, air would leak into the torpedo chamber, effectively recalibrating the depth sensor. The solution would not come until Hitler himself sarcastically asked whether they were firing torpedoes in proper conditions, i.e. underwater.

By mid-1939, these studies led to the development of the G7e/T3, a far more deadly weapon in the Kriegmarine’s arsenal that would come to wreak great havoc on the Royal Navy.

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