PISH - and I\'m not taking it!

[Rrickoshae]

well, doesn't look as if anyone knew what PISH (as in HESH etc) stands for so I'll have to tell you. It stands for Piercing Intelligent Squash Head. They were experimental in the 80s to try and develop a HESH shell that could differentiate between soft and hard targets, exploding on impact with a soft target rather than going straight through it but equally able to identify a hard target and act in the true HESH fashion. I have only seen them in 120mm calibre but in different lengths.
The success of the project hinged on being able to develop a fuze that do the 'intelligent' bit, and that is where it fell down - they couldn't, so it was shelved.
Photo attached of a sectioned proj and fuze, the Bofors gives scale.

 

[Rrickoshae]

lets see if the photo loads this time

 

[Chris 42 RQ]

Thank you for solving the mystery of that one!:cheer:

 

[SG500]

Picking up on this thread, can anyone explain how the PISH fuze works?

Attached are a couple of photos of one with a mills grenade for scale.

Dave.

 

[HAZORD]

This is the first time I've seen this post. I find it interesting that someone attempted to create a projectile that should squash tightly against an armored surface and also penetrate. The extra metal on the front would hinder the intimate contact between the squashed lump of plastic explosive and the armor it was intended to defeat, and trying to strengthen the nose of the projectile wouldn't seem to work when the projectile has such thin sidewalls, that the body would just mushroom out below the penetrating cap, increasing the diameter considerably and preventing further penetration. They might have had a fuze problem, but they also seem to have a physics and concept problem. Kind of like a heat seeking anti igloo missile.

 

[Snufkin]

This is the first time I've seen this post. I find it interesting that someone attempted to create a projectile that should squash tightly against an armored surface and also penetrate. The extra metal on the front would hinder the intimate contact between the squashed lump of plastic explosive and the armor it was intended to defeat, and trying to strengthen the nose of the projectile wouldn't seem to work when the projectile has such thin sidewalls, that the body would just mushroom out below the penetrating cap, increasing the diameter considerably and preventing further penetration. They might have had a fuze problem, but they also seem to have a physics and concept problem. Kind of like a heat seeking anti igloo missile.

I read it that a hard target would cause the usual HESH effect, but a soft target would cause purely an HE effect within the confines of the vehicle - the projectile was designed to penetrate soft-skins and light armour, then explode inside, rather than passing all the way through leaving just entry and exit holes. As for the fuzing I'd guess a small deceleration (soft target) would cause a few tens of milliseconds pyrotechnic delay (or whatever was needed) to result in a detonation within the confines of the softskin. HESH would be a few milliseconds to allow the charge to poultice on a hard target. Probably a tough balance to attain.

The acronym, like so military and modern comms acronyms, is not particularly helpful.




Tom.

 

[ozziammo]

Thought you were taking the PISH out of us there for a moment! LOL.

 

[EOD]

So the fuze has a soft/hard target discriminator?

 

[Snufkin]

So the fuze has a soft/hard target discriminator?

Yes. Without have a drawing to work with, it appears from Dave's photos to have a sensitive graze element (needle and creep spring) stuck on the back of the direct action HESH igniter.

On soft impact only the rear needle pellet (with the ball bearings) moves, against the creep spring, igniting a pyrotechnic delay (long delay*) contained within the big threaded forward needle holder. Flash holes either side of this second needle pass the flame to the detonator causing shell detonation (after a further short delay*) within the soft target.

On hard impact the whole tubular section containing both the needle pellets slams into the HESH detonator; obviously the rear graze igniter goes off and the long pyrotechnic delay starts burning, but that's irrelevant compared to the short* delay to enable poulticing of the charge.

Clearly the development aim was to produce a dual purpose round to replace two separate rounds (HE and HESH). (Given the limited 120mm ammunition storage in main battle tanks, it makes obvious sense to reduce the types of ammunition. Supply logistics are also eased.) The difficulty in fuzing was most likely selecting the appropriate long delay that would guarantee detonation within a whole range of soft skins, armoured personnel carriers, infantry fighting vehicles, etc.


*long delay is tens of milliseconds, short delay a few milliseconds





Tom.

 

[Old_ROF]

This is interesting. Was this work being done by RARDE back in the eighties?

I was under the impression that PISH stood for Product Improved Squash Head. The aim of the program was to update the round to enable it to be fired at a higher velocity, upto around the 1000m/s from ~700m/s i.e similar to HEAT round levels, to bring the performance level closer towards the fin round. It was given a nose cap to make it more streamlined to reduce drag and to enable to penetrate an initial barrier. This was to reduce time of flight and maintain the accuracy/consistancy levels of the existing HESH shell.

Obviously from what you have reported it also had this fuze development work also going on to enhance its capability more completely.

 

[SG500]

Thanks for all the feedback guys.
I've attached a few close up photos of the fuze.
Dave.

 

[HAZORD]

I can appreciate the alternate theory about the design. A problem that arrises from that is that the sidewalls are still to thin if you are going to push it at that velocity. The U.S. first HE projectile for the 90mm antiaircraft gun was the M58. The sidewalls were too thin and the projectiles would break up from the centrifugal forces. The Germans were able to make thin walled projectiles for their 88's, but the filler needs to have its own structure to keep it from pushing on the sidewalls.

 

[Snufkin]

This is interesting. Was this work being done by RARDE back in the eighties?

I was under the impression that PISH stood for Product Improved Squash Head. The aim of the program was to update the round to enable it to be fired at a higher velocity, upto around the 1000m/s from ~700m/s i.e similar to HEAT round levels, to bring the performance level closer towards the fin round. It was given a nose cap to make it more streamlined to reduce drag and to enable to penetrate an initial barrier. This was to reduce time of flight and maintain the accuracy/consistancy levels of the existing HESH shell.

Obviously from what you have reported it also had this fuze development work also going on to enhance its capability more completely.

Until reading the first post in this thread, I'd never heard the acronym PISH (or if I had I'd found it so meaningless it just hadn't registered) - Product Improved Squash Head sounds more plausible to me than Piercing Intelligent Squash Head, and a development programme under that name to improve the ballistic performance of the HESH round seems highly likely. It would also have made sense to evaluate different fuzing mechanisms as part of that overall programme. My take on the tandem needle pellets in the fuze body is simply one of casting an analytical eye over its construction, wherein its mode of operation appears fairly straightforward. The devil of this fuze is in the detail, i.e. in getting the first delay optimised to work for the majority of soft targets.

I can only assume RARDE was the main driver for this work back in the eighties. (I did have engineering involvement with RARDE in those early days of my career, but it was nothing to do with cannon projectiles of any type.)




Tom.