WP - illuminating or not?

Discussion in 'RLC' started by putteesinmyhands, Jun 27, 2006.

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  1. dingerr and I have been having a bit of a discussion regarding the luminary abilities of WP and it's time to start it's own thread to get a wider viewpoint.

    I've come across a few posts (mostly US blogs) that suggest that some US illuminating ammunition provides light from a WP composition.

    dingerr insists that WP is solely used to produce smoke, stating:
    While I would not disagree vehemently with the gist of dingerr's comments, I can see some holes in his arguments. These are:

    The British use of WP as a smoke generator requires the missile to burst apart on striking the ground, spreading the WP over a large area. In this scenario, the brightness of the flame is obscured by the smoke that spreads around it. Indeed, it is the brightness of the flame reflecting off the smoke particles that aids obscuration.

    Were the WP to be deployed in the base of a parachute-retarded munition, the ejected smoke would rise above the munition due to both thermal convection and also the descent of the munition. The smoke would therefore not obscure the light but would reflect the light towards the ground. To some extent this would provide less harsh illumination of the battlefield than is the case using British illuminating rounds.

    Because the WP is not burst from the projectile, I'd presume that the smoke would be less dense and a longer duration of illumination would result.

    So, has anybody any experience of a WP illuminating round? And are there any ATOs who can throw in some technical comment?
  2. Sympathetic_Reaction

    Sympathetic_Reaction LE Book Reviewer

    WP smoke rounds, both mortar and Artillery don't actually strike the ground and break apart, they eject WP canisters whilst still in the air, it gives a better distribution of smoke...but that was just a technical point.

    Phosphourus when it burns (on contact with air) does give off light, but it is pretty pathetic. It can be refined in such a way to give off less smoke and more light.

    The main problems with WP is the fact that is reacts very quickly to air and so is quite unstable to move around in anything but a nice solid container (so there goes your light weight hand carried light) it also gives of Phosphene gas which is toxic and also is quite expensive to manufacture.

    Magnesium and suchlike is generally cheaper, gives better light and isn't going to kill you or randomly explode if carried round in a lightweight container.

    generally WP is not nice, which is why it is being replaced by Red Phos...which is similar but less nasty.

  3. After 20 odd years working with ammo I can quite honestly say I have never come across WP used in anything but the smoke and incendiary role.

    I'm not saying it isn't possible, just highly unlikely.

    WP isn't that good an illuminating composition. It moderately bright enough initially (found out after prodding SIP grenades with a really long stick). Then is either obscured by smoke or the cake/residue that builds up on the surface in contact with air. It's this residue that means WP tends to be primarily used in bursting munitions where the phosphorus is blown apart into small pieces. This gives each piece a greater surface area in contact with the air which in turn produces a more rapid cloud of obscurating smoke/larger area of burning. If you were to have a solid lump then it would self extinguish as the outer layers are covered with the residue, denying oxygen to the fresh phosphorus beneath.

    Probably not too helpful but then I'll do some digging at work tomorrow...

    edited to add:


    a bit of light reading.
  4. It's going back 25 years since I last looked at a cutaway drawing, but I seem to recall that the 81mm mortar WP smoke bomb comprised a hollow casing filled with the WP composition and was fitted with a L35 fuze. This fuze initiated by striking the ground, detonating a small amount of explosive that broke the casing and caused the WP composition to spread over a wide area. It certainly had no means of dispensing canisters while still in flight.
  5. Cheers, apfsdsdu, but part of your argument is where I'm coming from. A parachute-retarded munition isn't going to be affected by the smoke as this either goes upwards by convection or stays at the same altitude (approximately) while the projectile continues its downward motion. While it would be useless for projecting light upwards, I can see that casting light downwards could be a possibility. The deciding factor is whether the WP burns bright enough to be of use.

    Your comment about the formation of residue is an interesting one. If the WP is enclosed within a casing and therefore has only one aperture to escape from, wouldn't this cake be continuously broken off as the WP burns, exposing more fresh WP? Alternatively, if the WP is mixed with beads of a material that expands on burning, the residue could be encouraged to break off more readily. Small iron, copper or aluminium pellets could achieve this (just a guess - it's what I'd try as a solution).
  6. To answer the question: Does WP burn sufficiently brightly to be of significant utility as a battlefield illuminant?

    Answer: No.

    As far more learned persons (above) have already stated, WP burns in air and produces shedloads of very hot smoke, which plumes rapidly, creating distinctive white columns. It is white due to the hygroscopic nature of the smoke, drawing in water vapour from atmosphere - hence it's white.

    The actual 'burn' is entirely confined to the surface of the WP in contact with free air - not very much - and contains nothing in the way of an accelerant or booster to improve light quality. For that, we tend to use aluminium powder and certain metal salts.

    Quick one on red phosphorus - it is just as effective but does not burn on contact with air. This means that mortar bombs are going to get a lot more complicated, as they will require a new SAFU system.

    Edited to add: It's also non-toxic, unlike WP and BE Smk...

    I'll get me coat.....
  7. Firstly i am an Ammo Tech (ATO if you must) and have been for a number of years.

    Secondly i have tried to avoid being too technical because i just know my fellow brethren will pile on me for being so anoraky, but hey ho here goes arms wide open. SO lets begin.

    Jones - WP munitions do not burst break out in WP canisters, they burst spreading the WP over a wide area thus exposing more of the surface area to air and producing a rapid, dense cloud of smoke.
    I presume you mean phosgene gas? WP does not produce phosgene gas when it burns this would make all WP natures chemical and that is very naughty and us Brits are good little soldiers. Also during their AT/ATO course students walk through a cloud of WP smoke and it is used as a smoke screen and therfore troops are exposed to it. Not heard of anyone suffering from pulmonary endema in either case. WP does not necessarily need a thick cased munition to be use/stored (i.e Grenade Hand Smoke No80 White Phosphorus (obsolete)). WP is surprising cheap to manufacture, more so than other chemical compositions, its expense is increase slightly due to the deleivery system required for WP munitions and also the fact that they have to be filled under liquid. Munitions do not randomly explode. WP cannot be refined in any way to alter its chemical state, it does not bind with other additives that may for instance produce different coloured smoke or reduce the smoke produced. Red Phosphorus burns to WP, but requires an external ignition source to initiate the chemical reaction.

    Is there anything if failed to correct you on?

    Puttees - I appreciate that a lot of the info you have collected is from US blogs, however these people appear to be the end user and not the chemists, munition designers or technicans, they do appear to be the normal blustering pontificating yanks. The trouble with thrying to contain the burning rate of WP to reach a desired effect is the fact that WP burns so hot that it easily burns through metal so it is difficult to contain it in an object and control the burn.
  8. Nice. Anoraky, but nice. :D
  9. Yes i know

    Now zipping anorak right up, deploying smoke and legging it.
  10. Oh Jeez. I've started one here.

    Having done some web searching, there seems to be a lot of contradiction about WP. Even the Wiki links don't agree with each other.


    Perhaps the spams use the term "illuminate" where we would say "identify?"

    I could go on, but I think this illustrates some of the contadiction.
  11. Why do you think we use WP mixed with HE on objectives?

    To mark the objective for subsequent attack from the air - they look really really bright through FLIR, and to identify the objective clearly for ground based sensors...and because chunks of WP whizzing about your ears isn't nice.

    Oh sorry - I mean we clearly don't do that. Ahem.
  12. Its not really contradiction. Its all about concentration levels. The first quote you posted appears to be worst case scenario. The second appears to be 'real life' what we would expect to be exposed to. I've been exposed to WP smoke quite a bit in the past so have many of my collegues to no apparent ill effect.
  13. Of course not. Dolly mix on Helicopter LZs to degrade the performance of the helicopters and confuse the pilot as to where the ground is, but switch to HE once they've landed. Shame about time of flight.
  14. Yes, I recall a mortar concentration where the wind changed direction during a mass WP shoot. Cough, cough, weep, weep, vomit - RUN!
  15. I nearly got brained by the base of an artillery smoke round in BATUS; I was told by a gunner that the round "functions" while in flight.