Hedgehog

The so called "hedgehog".......was not really a "depth" charge.....did it work magnetically, or some type of proximity fuse.....what set them off exactly.?
Thank You

 

Contact fuse. It only went BOOM when it hit something, so you usually knew when you missed and when you didn't, this allowed for quicker follow-on attacks. Also, since a "miss" did not generate an explosion, the sonar could maintain contact with the enemy submarine. With, the depth-charge, it usually took some minutes to reacquire contact, because the water was so disturbed by the DC explosion.

 

In addition it was fired off the ships bow rather than the stern. Reducing the time the submarine had to escape.

 

They seem so small when compared to the big drum of a DC.
I guess they made up for their size by exploding right on the Sub itself.?
In theory, was One Hedgehog capable of Destroying/Disabling a submarine.?
Thanks

 

https://www.youtube.com/watch?v=5kAj9syecU0

Precisely, one hit was all it took.

 

An attack with a Depth Charge: The Destroyer located the U-Boat, then increased speed - lost contakt because of the own noise - passed the position, released the DC and then lost contact again. The destroyer needed the speed, otherwise it could be damaged by the explosion.

With the Hedgehog you could attack the Subs without loosing contact and, even more important, you don't have to guess the exact depth of the U-Boat! German Subs used to dive deeper than the RN thought it was possible, below 200 metres the boats were safe.

 

The sub's inner hull, the pressure vessel, would already be heavily stressed...and the water would, like the waters of the German dams attacked by the Dambusters, "tamp" the force of the blast against the hull - thus meaning that it would take a quite small explosive charge to do the job...when applied direct to the target, which was ensured by the contact fusing

Depth charges were, on the other hand, a "proximity" weapon that relied on overpressure cracking the sub's hull.

It's really the same difference as a conventional explosive "bunkerbuster" cracking open a hardened target like, say, Libya's air defence command-and-control bunkers when delivered on the front door or down an air conditioning duct by precision guidance...and such bunkers otherwise requiring a nuke impacting perhaps a mile or two away delivered from a couple of thousand miles away. The smaller charge delivered right on the nose does the job of the much larger one designed to propagate a pressure wave

 

I see.......Thank You

 

The shape of the hedgehog projectile with its flat nose suggests to me that it could have been a shaped charge. I don't know if that's true, but otherwise why the flat nose?

 

It's not actually flat Nor was speed of travel through the water important, it was an even pattern I.E. spread of fall of shot that was.



As to what was UNDER that little cap on the nose...

 

While checking out the info on Hedghog at:
http://www.navweaps.com/Weapons/WAMUS_ASW.htm
I ran across Mousetrap which I was totally unfamiliar with. Essentially a rocket propelled version of Hedgehog that allowed it to be used on smaller ships.
This site mentions that there were cases of U-boats surviving multiple hits:
http://www.uboat.net/allies/technical/hedgehogs.htm

Here's another page with some info:
http://www.desertwar.net/hedgehog-weapon.html

 

I suspect that hits on places like the deck cannon, AA guns or even periscopes may have resulted in a non-lethal hit.

 

How powerful was it? I mean, in comparison?

 

I think one of the references above mentioned 30lbs of TNT or 35lbs of Torpex. Torpex was I think about 50% more powerful than TNT so the latter would have produced considerably more punch.
Looking at our old friend the 5"/38 the explosive charge varied from a bit over 2lbs to almost 4lbs or about 1/10 the above.
http://www.navweaps.com/Weapons/WNUS_5-38_mk12.htm
Looking at the US 8"/55 (the main guns of the Baltimore class) the AP rounds had about the same as the 5" where the HC rounds contained about 21lbs of burster so about half what's in the Hedgehog
http://www.navweaps.com/Weapons/WNUS_8-55_mk12-15.htm
The Alaska's 12" guns contained about half that for the AP rounds and about twice for the HC rounds bracketing the Hedgehog rather nicely.
http://www.navweaps.com/Weapons/WNUS_12-50_mk8.htm
Looking at a number of sources WW2 HE bombs tended to have about half their weight in filler which was usually TNT so 35lbs of Torpex is approximately equivlant to a 100lb bomb.

 

Thanks IWD

 

Torpex.......isn't that the stuff that went off, and killed Joe Kenned in that tragic, "remote" control Plane/Bomb that the Allies were toying with.?
It was a torpedo explosive, maybe.?
Thanks

 

It was a torpedo explosive developed during the war. From:
http://www.navweaps.com/Weapons/WTUS_Notes.htm

 

Thanks for the info.
Would love to watch some WWII videos with an explosive expert, and just Listen to them talk about what is going on the in film we see.......

 

Hedgehog equipped ships retained heavy depth charge batteries, up to eight throwers and 200 DCs in frigates or DEs. WWII hedgehogs fired directly ahead, so if they didn't hit or destroy the target, the ship was set to follow up with a depth charge attack.

By contrast, ships equipped with the Squid mortar carried a minimal DC armament, only fifteen charges with two throwers, enough for three five-charge patterns.

 

LWD, there's a bit of a difference between shells designed to burst in air...and bombs of course....and underwater ordnance like depth charges and Hedgehog. Ideally - in the air, shells and bombs' burster charges are tamped momentarily by their casings...THEN when these burst, the pressure wave created and expanding rapidly outwards is fronted by the casing fragments. Apart from actual overpressure, and fragile objects damaged or destroyed by the pressure wave....it's the expanding..."shell" (sic) ...of fragments that do the actual destruction.

Underwater, the water itself does the tamping....and would also VERY rapidly rob any casing fragments of the velocity needed to do damage. Hence "contact" explosive devices, or ones designed to explode very close to the target, are what's necessary - or of course devices like depth charges with VERY large amounts of explosive in the explosive-to-casing ratio that are big enough to reach out and touch over a limited distance

For an example of the problem of shells and bombs going off underwater - in 1940 and 1941, when the Admiralty had the Fleet Air Arm test its gravity ordnance against the sort of single-skinned steel hulled barges likely to be used in any invasion - it took a 250lb iron bomb of the day to go off within just fifteen feet of such a hull to do "catastrophic" damage likely to sink it. And that is remarkably close for anything except very accurate and VERY practised lowlevel divebombing to deliver.