Military-Grade Awesome

Sub-Sonic: Britain’s Hedgehog


Yesterday we looked at a less than successful weapon developed by the awesomely named Directorate of Miscellaneous Weapons Development. Today, we look at one that was much more successful. Not to be confused with the Soviet Fire Hedgehog, the British Hedgehog was an anti-submarine weapon that actually proved more deadly than depth charges.

Depth charges work by exploding near a submarine. The attacking ship has to know the depth of the target submarine and a pressure fuse is set. Due to their size — equivalent to a 600 lb. bomb in some cases — a depth charge doesn’t have to be extremely accurate and repetitive depth charge explosions near a submarine’s pressure hull can eventually cause it to fail. The problem is, the depth charge still has to be close enough that the pressure wave impact on the submarine isn’t overly dissipated by the water. They also go off no matter what and the noise can take 15 minutes to dissipate enough for a sonarman to hear the enemy sub. In this time, the sub may have escaped. Finally, the sub can hear them coming. They hear the splash and the metal canister falling through the water. If they are deep enough, they can potentially evade the depth charge.

So, how do you make it better? Major Millis Jefferis decided you start with the spigot mortar design from the inter-war years. A spigot mortar consists of a base and a rod, or “spigot”, onto which the mortar would fit. The propelling charge would act against the spigot launching the mortar. Maj. Jefferis thought, “Why not line up a bunch of these and fire them into the sea?” So, he did just that. Without the mortars loaded, the rows of spigots resembled a hedgehog, hence the name.

The spigots were arranged so that the Hedghog would fire 24 mortars in a 100-foot diameter circular or elliptical pattern roughly 250 yards ahead of the attacking ship. The mortars were equipped with contact fuses so they would not explode unless they hit something. About 25% of the time that something was a submarine. Depth charges, on the other had, had a kill rate of about 7%. Since the mortar wouldn’t explode unless it hit an enemy sub a miss would not “blind” a sonarman. Hence, he could continue to track the sub and after a 3-minute reload of the Hedgehog they could fire again. Only one or two direct hits by a 30-lb Hedgehog was sufficient to sink an enemy sub.

The Hedgehog was so successful that it was used in some form or another into the 1980s by the Brits, Americans and Soviets. Variants were even adapted for air launch and ground launch for clearing out mines and enemy encampments. It was even adapted for use on Australian Matilda tanks towards the end of the war.

[Image Credit: Historik Orders]