The Hedgehog in WWII

by P. T. Deutermann

My latest novel, The Last Paladin, out this month, is based on a true story of WWII. In this book, the USS Holland (DE-24), a World War II Atlantic Fleet destroyer escort, spends years in an unforgiving battle for survival against the German U-boats of the North Atlantic. Looking back through modern maritime history, much has been made of the necessity to have a muscular anti-submarine warfare capability if you’re going to conduct wartime operations at sea.

Every ship on the surface of the world’s oceans is vulnerable to submarines, those silent, almost invisible ambush killers, who make their presence known when one of your ships suddenly explodes. Submariners happily classify all ships into two categories: submarines and targets. Modern torpedoes are so powerful that the shock from a hit can both break the back of the target ship as well as the legs of everyone onboard, dooming them all to go down with the ship. 

U-Boat, Type XXI.
Author: Clemens Vasters.
This file is licensed under the Creative Commons Attribution 2.0 Generic license.

The Germans introduced the world’s Navys and merchant marines to the strategic consequences of being unprepared to face unrestricted submarine warfare. By 1945, they had the most advanced submarine on the planet, the Type XXI, with a superbly streamlined hull, an advanced snorkel underwater breathing system which meant they never had to surface unless they wanted to, and improved longer-range torpedoes.

The Allies had long since been forced to move vital cargo over the seas in large, slow convoys, where it became theoretically possible to offer better protection. But it wasn’t until they integrated carrier-borne air into convoy defense that they finally were able to move to the offensive, search out, and then defeat the dreaded U-boats. The Germans finally gave up on submarine warfare when 75% of the boats that went out never came back. 

The Hedgehog, a 24-barrelled anti-submarine mortar mounted on the forecastle of HMS Westcott.
This image is in the public domain via Wikicommons.

One of the other weapons that turned the tide was a ship-mounted mortar system called the Hedgehog. Invented by the Royal Navy, the Hedgehog projected a pattern of 24 small depth bombs** out in front of an attacking destroyer who’d gained contact on an enemy submarine.  The crucial feature of this weapon was that it didn’t explode unless it actually hit something, unlike depth charges, which would all go off regardless and so badly roil the underwater acoustic conditions that the submarine, if not actually hit, could usually escape. But if even one or two Hedgehogs hit, the submarine was almost always doomed. The mortar bomb would punch a 3” to 4” diameter hole in the boat’s pressure hull. With the submarine down at 250 to 300 feet, (having gone deep to evade attack) water would enter the pressure hull at about 400 gallons per minute. This basically unstoppable flooding would instantly begin to raise the atmospheric pressure, and thus the temperature, inside the submarine. As the water continued to roar in, the boat would lose depth control and settle even deeper, increasing the rate of flooding. Within a few short minutes, the temperature inside the boat would climb above 200 to 300 degrees, searing the lungs of the crew and rendering them all dead. The boat would then continue sinking until the pressure hull collapsed entirely. 

If the escorts heard no bang, they’d simply make another run, since the sonar acoustic conditions remained as before, undisturbed. If they did hear a couple of bangs, they could simply leave. That submarine was never coming back.  

Photo Credit: Cynthia Brann

P. T. Deutermann is the author of many previous novels including Pacific Glory, which won the W. Y. Boyd Literary Award for Excellence in Military Fiction. Deutermann spent twenty-six years in military and government service, as a captain in the Navy and in the Joint Chiefs of Staff as an arms-control specialist. He lives with his wife in North Carolina.