Time for the 120mm mortar?

Discussion in 'Infantry' started by Far_King_L, May 6, 2008.

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  1. We have had the 81mm since the 1970s, and I know it has given sterling service

    I am also aware of eg the lethal and blast radius, planning range etc but will not discuss these here

    When introduced it would have been intended for use against the Soviet hordes should they cross the IGB, but looking at the last ten to fifteen years, most warfighting has been of a different nature.

    There has been a great deal of warfighting in eg. Bos/Kos, and obviously the current main effort is in Afghanistan.

    Would the extra firepower of the 120mm now be a worthwhile asset?

    I know that in FRY one of the main causes of death has been the 120mm; it also seems that the range at which targets can be acquired in Afg can vary greatly, and do not doubt that the extra range of the 120mm ( 7-8 km ) could be well used.

    I have not seen the 81mm used with BULLDOG but there is already an OTS 120mm SP twin automatic mortar in use with the US, Canadians etc and it seems to me to be a logical; step to at least consider it.

    There is a tracked, armoured mark avaiable ( See here ) so it offers protection.

    The 81mm is a great weapon system; battle proven and effective, but AFAICT we do not have it in any mobile platform ( I'm deliberately excluding the ancient 432 series, but stand to be corrected. )

    Double the blast / lethal radius; greater range; armoured vehicles OTS...

  2. 81 is man portable - I doubt 120 is. It might be useful but it would be an extra capability rather than an 81mm replacement. Would probably end up being an asset at a higher level than Bn.

    Then again, I may be talking out of my Arrse.
  3. Qiute right, 81mm portable, 120mm no way. Looking at how things are done in Afg a lot of moves are made by vehicle; an FSB could be set up with one of the 120mm SP carriers while the dismounts close in. The Germans have (* IIRC ) a towed 120mm.

    They also have ( or certainly had ) 20mm cannon. That gets VERY serious.
  4. Once you get past the range and weight of the 81mm, you're into the realms of artillery.

    The 81's advantages are that it's man-portable (so it's a go-anywhere system) and can keep up with, and is dedicated to, forward units. It's fast to set up and, although inaccurate (as all mortars are, due to the high trajectory) can be corrected quickly onto target. It's inaccuracy becomes an advantage when engaging targets over a wide area - hordes of enemy infantry advancing across hard open ground being a prime example.

    If you can engage the enemy in the direct-fire role or with low trajectory, artillery start to win on speed while howitzers take care of the indirect fire tasks. Artillery is more suited to individual targets - hardened strongpoints, for instance - and ought to risk less collateral damage.

    IMHO, going to 120mm mortars would have benefit over 81mm only if they were mounted, either on vehicles or trailers, at which point artillery would prove more versatile.

    Big bombs create big bangs, but would 120mm bombs at 4 rounds per minute be more effective than 81mm bombs at 12 rounds per minute? I doubt it.

    Horses for courses. There's a reason why the British Army puts up with the RA.
  5. Hello,

    A larger mortar calibre has major advantages.
    For a given level of effect,it costs less and requires less effort of the crew to fire one large bomb instead of a number of smaller ones.
    Even with a lower rate of fire in bomb terms,the larger mortar can have a greater rate of fire in effect terms.
    The larger bomb will also be able to provide penetration which could not be easily acheived with a number of smaller bombs.
    If we wish to develop guided mortar bombs,it is easier to accomodate guidance within a larger bomb.
    It is also easier to justify the expense of guided bombs when they have greater potential for effect on target,particularly with shaped charge rounds.

    On the other hand,those armies which use 120mm mortars usually retain a lighter mortar as they still need something man portable.
    The American Stryker 120mm mortar carriers for example also carry 60mm mortars for the dismounted role.
    Man portability is one of the main reasons for having a mortar instead of a howitzer.
    Neither 120mm mortars nor their ammunition supply could be considered man portable.
    If you have 120mm mortars,you also need something lighter and having two mortar systems is more expensive and less flexible than having one which can do both jobs.

    There is an alternative.
    Our current 81mm mortar is far lighter than the 3" mortar it replaced,despite having far greater performance.
    Design,manufacturing and materials technology has advanced in the last thirty years.
    Were we to develop a new 81mm mortar today,it would be lighter than our current one.
    Alternatively we could have a larger calibre mortar of similar weight to the 81mm.

    Sustained mortar fire requires an environment where there is a secure supply of bombs and limited threat of counter battery fire,defending a fixed base in Afghanistan for example.
    Tactically and logistically,foot mobile operations against a more capable adversary would require more of a shoot and scoot approach.

    From a design perspective this has advantages.
    The weight of a mortar is highly influenced by the pressures and temperatures it must withstand.
    These are in turn dictated by the range and rate of fire we demand of the weapon.
    The less demanding we are in these areas,the lighter a mortar can be.

    A four inch mortar bomb would weigh roughly as much as a brace of 81mm bombs.
    However,it would require less effort to pack,unpack,fuze and fire than the two 81mms.
    It would also likely cost less,have a greater lethal area and greater penetration than two smaller bombs.

    Thus a 4" (approximately 100mm) man portable mortar may be a practical alternative to 81mm and 120mm mortars.

    A number of 98mm and 100mm mortars are currently in service,the Poles have the M-98 and the Chinese have these:



    I have no doubt we would be able to design something a little lighter.


    P.S.Should this be in the calibres thread?
  6. Good points, but how fast can the No.2 stoke 4" bombs into the mortar? If they weigh twice as much as 81mm bombs, the No.2 will tire, resulting in a lower rate of fire. Thus the 81mm will be more effective against soft, wide-spread targets.

    For a hardened, immobile target, accuracy becomes critical. To reduce the effects of meteor, low trajectory is preferred due to the lower time of flight, giving the edge to artillery. The larger caliber mortars, even if guided, only come into play if the target is in dead ground. The competition is then large calibre mortar versus howitzer and the versatility of the howitzer will win.
  7. I'd dispute this.

    The two 81mm mortars would be packed, unpacked, fuzed and fired by two crews and so would be faster than the 100mm mortar.

    Also, two 81mm bombs, falling 30-60m apart would have a larger lethal area than a single 100mm bomb.

    Don't forget the logistics. If you go larger than 81mm, you're into the realms of requiring a separate vehicle for ammunition carriage. So you're doubling the crew and equipment for the sake of a bigger bang that potentially has little more effect.

    I also wouldn't particularly fancy digging out the baseplate of a 100mm mortar after half a dozen rounds, the 81mm can be bad enough! The solution would be for the 100mm mortar to be vehicle-mounted, but by this time, it probably becomes more economic to use an AS90, shared over a wider area of the battle front.
  8. The current system works fine and fits in well with the other systems we have to deliver indirect fire at progressive, but overlapping ranges. Thats why they haven't wasted money on anything new.

    A 120mm will have a max range of about 10km with a 105mm 15km. The 105mm also has greater accuracy. Logistically 105mm is also easier to move and i have a strong suspicion that the ammunition would be cheaper.
  9. Hello putteesinmyhands,

    the Poles claim a lethal radius of 80m for their 98mm mortar,40m is a commonly quoted figure for 81mm mortars.
    I will happily be corrected if those figures are awry.
    However,if they are correct then doubling the lethal radius would give us four times the lethal area for the 98mm bomb.

    The 98mm bomb would weigh twice as much as the 81mm so we could carry half as many but,if the above figures were correct,that would still give us double the lethal area for the same weight of bombs.
    Alternatively we would still get the same lethal area covered per minute with one quarter the number of bombs fired per minute.

    Again,that all depends on how accurate those lethality figures are.

    When we get to the point of a mortar requiring a vehicle to carry or tow it then we may as well have a howitzer but it is worthwhile to go as large as is practical with man portable mortars.
    I think 4" is the practical maximum calibre for a manportable mortar.


    Edited to add I am hoping dingerr will be able to shed some light on the accuracy of the lethal radii quoted above.

    Edited again having reread putteesinmyhands last post,just to be clear I am comparing one 4" mortar and crew versus one 81mm mortar and crew.
  10. From the point of burst, the lethal radius is probably about 40m, as you say, with injuries extremely likely to twice that distance. But as the mortar is a (beautifully) inaccurate weapon, the second bomb that falls could well be 40m from the first, and the third another 20m away in a different direction. Add in the common practice to use mortars in groups and make use of the high rate of fire, and you neutralise a very large area in a very short space of time. (Then you make an equally hasty escape).

    If you double the amount of explosive, you don't double the kill radius - that would take four times the amount of explosive - it's an area, so effect is roughly proportional to the square.
  11. Sorry T6, i don't have that info. Someone with the Inf 81mm Mor Pam might be able to enlighten.

    The lethality radius is only part of the story though. I feel that a greater weight of fire is preferable to keeping the enemy's head down. Also a larger lethal radium means that any supporting barrage has to be lifted sooner as friendly troops advance.

    (Check that out! and i'm only a fat loggie.)
  12. That's not fair. The 100mm mortars you linked to have a crew of 7-9 - comparable to the crews of two 81mm mortars. :)

    But it doesn't alter the fact that the 81mm mission would be complete while the 100mm crew are still hauling ammo to the firing point.
  13. You have to be carefull in computing exactly what the lethal radius of a particular bit of ordinance is. It's all well and good to claim fourty meters for an 81mm high explosive round but that performance was calculated under pristine conditions on an open range and even then... is very suspect as all it means is that some chunks of schrapnal retain enough energy to puncture a human's hide at that distance from the point of impact. I'd say fifteen meters is more appropriate of an area of effect for that round of ammunition... and even that is being liberal because one's enemy rarely hang out in wide open spaces standing straight up to provide a good target to knock over. Unless one is saturating an area with cluster munitions like IDPCM it's a bad idea to assume your barrage will be effective via a mathmatical formula.

    Far as the 81mm vis a vis 120mm debate is concerned... both are very effective indirect assets when utilized properly and as mentioned before, there is a trade off of mobility for firepower between them. Like the old four duece (4.2" or 107mm mortar) the US Army has made the 120mm either a towed or vehicle mounted asset (depending on the unit involved... only the 101st, 82nd, & 10th ID use the towed version) which more or less eliminates the ammunition constraints as no one is required to hump the rounds. The 81mm system on the other hand is occasionally carried although even the light outfits tend to find motorized means to transport the tubes and baseplate when possible.

    Speaking of 81's... the US Army has made changes to the company level mortar section. In my day all they had were 60mm tubes capable of direct lay in hand held mode as well as indirect but 81mm systems are sharing space with the 60's during deployment. Apparently the 81's are used in established positions while their little cousins are attached to the individual platoons as needed.
  14. Hello putteesinmyhands,

    if that is the case,there may well have been a little "sales patter" in the Polish figures then!
    Well spotted on the crew requirements,they quote 5-7 men for their 82mm mortars.

    My thinking was that we could get away with the same crew for a 4" as for the 81mm,providing we could make one light enough.
    One man would carry a single 4" bomb instead of a twin pack of 81mms when foot mobile.
    Even if the bombs weighed more,there would be fewer bombs to fuze and load per minute.

    The logic for that whole scheme was dependent on the bigger bomb having a sufficiently larger lethal radius to offset the smaller number of bombs being fired.
    I had come across some figures in the past which led me to the conclusion that it would be.
    However,if that is not the case,I happily stand corrected.

  15. Even though technology has advance, there would be little weight reduction in bombs due to the body bring required to produce the shrapnel and ultimately cost.

    A welcome addition to the 81mm HE would be the implementation of a prox fuze. Shouldn't be too difficult as the 60mm uses a M734 that has Prox (1-4m burst height), near Surface Burst (0-1m) Impact and also Delay (0.05secs). On the face of it i cannot see compatibility being too much of a problem as both 60mm and 81mm use the M935 (unfortunately!).