35lb AS Bomb Mk I/II

[DWG]

(This is one of those topics that seems to fall between boards, Missile Projects comes closest, AFAICS)

I recently came across the USN's 1946 'British Explosive Ordnance', which turns out to be one of the most fascinating things I've read in a while - there's a staggering number of UK cluster weapons, for instance. There's a copy online here http://www.lexpev.nl/downloads/britishexplosiveordnance1946.pdf , and similar documents for the other WWII nations.

One project that particularly caught my eye is the 35lb AS Bomb Mk I/II in the Obsolete Weapons Chapter. At first glance this seems to be a Hedgehog bomblet, and, while I've seen air-delivered Hedgehog proposed in an alternate history project, I'd never come across any evidence that it was tried for real. But then it struck me that the weight doesn't fit. Most references I've seen for Hedgehog give the weight as 65lb, with a 35lb warhead, and even assuming a drop in weight due to not needing the propellant charge, you aren't going to get the structural weight down to zero, and warhead weight of the 35lb AS is actually given as 16lbs of RDX/TNT 60/40. So does this mean there was a predecessor project to Hedgehog using a smaller bomblet? Note that the 35lb AS Bomb Mk II is specifically identified as a shipboard-fired version.

Googling around turned up a few more pages, mostly frustrating references to bits of the National Archives that haven't been digitised as yet - such as trials of an 8 round dispenser intended for Halifax, but also an IWM page on the weapon http://www.iwm.org.uk/collections/item/object/30023796 which includes the fascinating detail that operational trials on Hudsons in early 1943 may have resulted in two kills. http://uboat.net/boats/u558.htm lists an attack on U-558 by a Liberator dropping 24 weapons, and having a hang-up on a second attempt, while http://uboat.net/boats/u628.htm is a kill, but with the coup de grace from airborne depth charges after an initial attack with 35lb AS Mk I - this attack on 3 Jul 43 is stated to be the first operational use, again from Liberator.

Really interested to hear if anyone can clarify the relationship between 35lb AS Bomb Mk I/II and Hedgehog.

 

[CJGibson]

Might this be related to it? I found this pic in a photo bin at a show and know nothing about it.

Chris

 

[DWG]

Interesting shot!

Scaling from the bricks, I make the rear bomblets 44 pixels in diameter and the bricks in the middle course at bottom right of the hut 9 pixels. A standard house brick is about 2.5 inches, so that puts the diameter of these bomblets at about 11.25 inches.

Alternatively, if we assume that's a standard 35 inch high 55 gallon oil drum at the extreme right (I'm not 100% sure it is, but it certainly could be), that's 133 pixels(-ish!), which scales out at the bomblets being 11.5" in diameter.

But if we assume the light band on the bomblets is 1", which it would be for a 35lb AS bomb, then I measure the front column of bomblets 54 pixels high and the band 8 pixels across which gives us about 7".

British Explosive Ordnance puts the diameter of the 35lb AS Bomb at 7 inches, the IWM page on the Hedgehog bomblet here http://www.iwm.org.uk/collections/item/object/30023797 gives the diameter as 178mm, aka 7 inches, and various references suggest 7.2" (a traditional British calibre).

I've realised in looking at this that the fundamental difference between Hedgehog and the 35lb AS Bomb is that Hedgehog isn't a shaped charge, which accounts for the different warhead weights in a similar form-factor, and explains why Hedgehog is flat-nosed vs the conical-nosed AS Bomb.

Markings on your picture could be consistent with the 35lb AS Bomb, which is supposed to be dark green overall with a 1" red band and a 1/2" light green band. The light band could be red, and I think I can see a slightly lighter than the base-colour band forward of it, but that looks to be the same width as the more obvious band, which is inconsistent. What's definitely absent is the 'cylindrical nose attachment' - a short band tacked around the body and projecting slightly forward, which I suspect is intended to prevent richochet from the surface of the water - there are similar features on several other British weapons. Whether that would be there on the AS Mk II ship-launched version I don't know, Hedgehog doesn't seem to have it - possibly because the entry angle of a ship-launched weapon is more predictable. I can't see suspension lugs on any of the bodies, which could be another argument for them being 35lb AS Bomb Mk II.

However that leaves us with the diameter of the bomblets in your picture. I'd initially decided my scaling was at fault, or that it's a non-standard brick, but then realised I could use the oil drum to scale from as well, and both of them giving the same answer suggests this may well be something larger than 35lb AS or Hedgehog. But then the light band gives the correct 7" (but only if it is actually 1" wide). Another anomaly is that British Explosive Ordnance says the tail on the 35lb AS is six-finned. It's difficult to be sure, but I think the tails in your picture are 8-finned.

They're clearly based on the same design concept, but I really can't make my mind up as to whether these are the 35lb AS Bomb or not.

But thanks for putting it up!