Since 1939 Karl Donitz's U-Boats had been the terror of the seven seas but innovative new technology would end "The Sea Wolves" reign of destruction.

Since British Prime Minister Churchill declared war on Hitler's war machine, the sea's surrounding England and beyond became a watery grave for any ship military or otherwise that was suspected of supporting or supplying the isolated island nation.

Winston Churchill's first effective way of protecting cargo ships was to establish convoys to guard the valuable shipments essential to England's survival.

Any ship sailing alone was easy prey for Karl Donitz's ruthless "Sea Wolves" and their U-Boat captains who were eager to add another kill to their already impressive list of vessels and tonnage of supplies resting on the oceans bottom.

This approach helped reduce the kill ratio and allowed escorting destroyers a chance at retaliation. But still the U-Boat’s managed to maintained the element of surprise and could play cat and mouse with the convoys.

The method of attack first developed by Winston Churchill to battle U-Boats was “Depth Charges” the process was affectionately dubbed by mortar crews as “Tossing the Cans” in which canisters filled with explosives were launched from the deck of the pursuing war ships, the mortars that fired the loads were called Y-guns.

The use of depth charges was somewhat limited however, due to the need for the caustic cans to be very close and directly over the submerged U-Boat to be effective.

Later in the struggle a more effective weapon was created by the Allies called a “Hedgehog.” This new tool of destruction fired a salvo of 24 small explosives in a roughly circular pattern over a wide area.

The vicious charges could be fired up to 250 yards ahead of the attacking ship and the armaments were equipped with fuses that only ignited upon contact.

This increased the success of Allied submarine killers and having the misfortune of coming into proximity with the hedgehog’s volatile grenades was almost always fatal.

The further improvement and progress of “Sonar ” made it more difficult for U-Boats to hide. Sonar used sound impulses that reflected off objects and when connected to a compass would give the direction the U-Boat was roving and the time between transmissions and its echo exposed its range.

Sonar had it’s limitations though, the farther away a submarine was from the hunting vessel the more likely that it would be discovered and the closer a U-Boat was the less chance it had of being spotted due to the narrowing of the sonar’s beams.

The second major disadvantage of sonar was that the device could only be used to detect submerged crafts and any U-Boat on the surface was undetectable.

Commodore Karl Donitz ordered his “Sea Wolves” to attack at night and from the surface in order to avoid the Allies use of Sonar to track them.

This presented U-Boat commanders with several advantages. On the surface, U-Boats could travel faster, up to 18 knots, and with darkness as a shield were less visible and venerable to Allied counter measures.

But the technological advance that sealed the fate of the U-Boats was the development of an improved radar system that Winston Churchill had his scientist working on that used Microwaves. It was called the “Resonant Cavity Magnetron” and was light years above the traditional long-wave radar used by both sides.

With this finely tuned microwave radar device installed on Allied ships and planes they could pin-point the location of German U-Boats with extreme accuracy and when their locations were radioed to Allied bombers it was like a turkey-shoot.

By mid-1943, the now Rear Admiral, Karl Donitz was forced to swallow his boastful quote made earlier in the war “An aircraft can no more kill a U-Boat, than a crow can kill a mole.”

The U-Boats supremacy and deadly toll had at last come to an end. Winston Churchill had defeated Germanys U-Boats with science and technology, and the allies had also started building sleek and fast destroyers able to reach speeds of up to 24 knots and capable of better defending merchant convoys.

From 1939 through mid-1943, Admiral Karl Donitz's “Sea Wolves” had devastated shipping lanes the world over, and had been responsible for the loss of thousands of lives, millions of tons of cargo, and the sinking of thousands of ships from one end of the globe to another. And all this detruction had been thwarted by a little box that used microwave radar called a "Resonate Cavity Magnetron."

Reference:

Pitt, Barrie “The Battle of the Atlantic” Time-Life Books 1977