2017/01/21

42° elevation tank turrets

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There's a twin autoloader 120 mm mortar turret called AMOS that captivated the imagination and fascination of AFV fans for a decade or so. I was never a fan of it, not the least because of its price tag of € 2+ million for the turret alone.



It doesn't use standard munitions and its supposedly impressive rate of fire of up to 16 rounds per minute from two barrels combined is exactly the maximum rate of fire given for a single ordinary towed, manually operated mortar tube of the same calibre.
Meanwhile, twin tubes is massive overkill for direct fires on ground targets. 

By the way, the Swedish army is adding new CV90-based mortar vehicles soon, and they're not going to use AMOS, mostly because it's too expensive.

I think the way to go for 120 mm self-propelled mortars isn't a super-expensive AFV, but pretty much the standard APC with roof opened and a turntable with automatic tube laying for a (exchangeable) manually muzzle-loaded 81 or 120 mm mortar tube. Essentially what we've had during the Cold War, modernised with CARDOM. The real advance in indirect mortar fires of the past 30 years has been automatic tube laying, after all. This enables higher rates of fire and slightly more complicated fire missions such as MRSI or shooting rounds in optimised impact point patterns at short ranges.

Mortars fired from opened rooftops always shoot in the upper register, above about 43° elevation. This is high angle fire and many people appear to believe that it's unsuitable for direct fire. It's not; direct high angle fire is possible. Moving targets and vertical target objects (such as most walls) are  unsuitable for high angle fires, that's all.

So there's this idea that direct fire capability is valuable for a mortar carrier, and I largely disagree. Direct fire by a mortar carrier should be a last resort for self-defence or defence of nearby forces that badly need direct fire assistance in their defence. Multi million Euro AFVs that are indispensable in the indirect fires role will not be sent into voluntary direct fire combat missions often in actual combat anyway. Any such concept is bound to be limited to anecdotal direct fire actions.

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There is a case that can be made for a hybrid AFV, of course. Imagine some mobile army unit operating in rural areas of Africa. It could have 81 mm mortars for illumination and short range indirect fires and some AFVs with 105 mm guns capable of dealing with everything but post-1977 tanks. Two such mobile units may operate together, always ready to assist each other by fires, medical care or manoeuvre and subsequent line of sight combat. Surely, those forces would not refuse having some additional indirect fires capability without adding any vehicles?

The answer to such needs (and many scenarios in mountainous regions) is already available, and it's not AMOS. Cockerill has (had for years) light and medium tank turrets on offer that allow a 105 mm high pressure gun to shoot at up to 42° elevation. I was unable to get an answer on why the range is still limited to 10 km in their data sheets (should be more like 18-23 km with that gun, that angle, HE shell* and full charge), but 10 km is the range given for some of AMOS' munitions as well.

Back when I first contemplated writing this article I meant to write about the Cockerill CT-CV 105HP turret, but this appears to have been superseded by the XC-8-105-120HP turret. The changes appear to be about layout (sensors etc.) and the inclusion of the 120 mm tank gun option.



I'd love to bash their marketing for three reasons, but I won't because I'm using their photos here.

The current XC-8something turret is about the same, also with 10 km indirect fires range. These turrets have a bustle-mounted autoloader, but I still suppose that semi-fixed rounds could enable it to serve as auxiliary SPGs at times. The rate of fire wouldn't be extreme, but I suppose munitions resupply is a much bigger issue anyway.

XC-8 105-120HP turret
I have an interest in such dual use turrets for multiple reasons. A marginal reason is a theoretical anti-air capability, and another marginal reason is an irrational technology fascination, but the main motivator is that this makes tanks potentially useful during much more of the time.

Tanks are usually employed in either movement/assault or overwatch, and most of the rest of the time their crews are either resting, reloading or doing maintenance work. This is fine in most doctrines, though the quantity of videos showing tanks hit by missiles in Syria and Yemen while they're stationary and apparently on overwatch duty is appalling. Tanks on routine overwatch duty should be in a fully concealed position with a separate (or mast) sensor in operation (or at most the sensors mounted on top of the turret showing). Hull down positions are acceptable only for short times during which the crews can be attentive enough to react to incoming missiles in time, preferably with engine on idle.

My studies of operational art have led to my opinion that delaying missions should be the most common missions for ground combat forces, and might be central to "winning" a campaign. Furthermore, I concluded that tank forces should not be in the first layer of delaying efforts, and the powerful bulk of tank forces shouldn't be in the second layer either. Even when the main tank forces enter combat it shouldn't necessarily be the classic heavy cavalry-like tank charge, or even only the more realistic and historical advance into line of sight firing positions. It would be very nice if they were useful without line of sight as well.

It's near-impossible to synchronise mobile operations so well that two tank battalions or companies could converge on one hostile force and come into line of sight at about the same time. A battle between two tank companies could be over in seconds or minutes, so a second converging company might be of no use in this. (This is different from multi-axis ambush situations such as the L-shaped ambush.) To converge forces on one target force makes sense at the higher level to overpower the defensive capacity, but at company level it's too difficult to get the timing right, particularly if the opposing force manoeuvres unpredictably.
Now imagine the second tank company made it to within 3 km, but has no line of sight. It could at least give indirect fire support if it had this capability.

The high angle firepower will be more attractive to most people in the context of actions in mountainous areas and urban areas, of course. You can think about such situations by thinking about a single tank, and any hypothetical scenario that works on such an elemental basis is more accessible and convincing by default.

Now don't get me wrong; I don't claim that the XC-8-something turret with its many expensive electronics (gunner's thermal, commander's thermal, laser warner etc) for duel situations would end up costing less than an AMOS turret. It's a direct fire (duel) turret with some indirect fire capability. AMOS is an indirect fire turret with some direct fire capability. My point is that the widespread fascination with AMOS is irrational, and a direct fire turret with some indirect fire capability is a more sensible concept. Indirect fires capability with a little direct fire capability can be had relatively cheaply; combine a 120 mm mortar with CARDOM and a folding roof APC that can withstand the firing shocks.

S O
defence_and_freedom@gmx.de

P.S.: Don't get me started on AMOS as tank killer due to STRIX. It's not. STRIX can defeat stationary tanks, but the footprint (the area it is looking at to find a target) is so very tiny that it's all but useless against any but stationary tanks.

Furthermore, I understand that the 105 mm gun's rifling may  be an issue for the variable propellant charges in semi-fixed rounds. Dispersion am be worse than with an optimised SPG gun design with some charge strengths.

*: They don't tell about HE cartridges as one of the cartridge types for those turrets.
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6 comments:

  1. The XC-8-120HP do not have the high elevation, this is only a feature of the 105mm Turret.

    In all other points i can only agree with you. Such a indirect fire capacity would also be especillay useful for the support of infantry and other arms, especialy in assymetric warfare in which the enemy would avoid the tanks and attack other parts of my troops. With a indirekt fire capacity the tanks could assist then in anymay.

    The Joint Fire Support would become stronger in every aspect if more systems could act NLOS.



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  2. The Strix never was a thing, it's a unicorn only existing in brochures. Your idea is quite intresting.

    In Finland Amos is purely for indirect fire and would next to never be used for direct fire in other than self-defence. All mortars have direct fire capability but most people don't realise that it's still shooting at a high angle.

    If Cockerill could demonstrate succesfully the dual purpose capability they would attract lot of attention. I'm all for dual-purpose equipment as long as they can perform reasonably well on both. As for caliber and dual usage, I think both will suit reasonably well for light motorized infantry in mobile defence and hit&run missions. Either the turret can provide flanking shots or indirect fire or direct fire support for attacking say artillery battalion.

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  3. What do you make of the new 125mm Chinese gun ? it seems to be designed to be used in the way you suggest.
    http://www.popsci.com/china-builds-worlds-fastest-tank-gun-then-tries-hide-it
    I guess we will see a new Armored vehicle for it soon or maybe just a new turret .

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    1. That split carriage is likely little more than a testbed.
      The gun looks like optimised for tank duels in open terrain. The barrel length is going to be a huge manoeuvrability issue with trees, walls etc. 120 mm L/55 is already at best borderline.

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  4. Why not approach this from the opposite direction?
    The Gvozdika SPG has proven a valuable asset in the Ukrainian war. It is capable of both indirect and direct fire. By no means is it a substitute to an actual tank, but it has proven fairly capable of suppressing AT positions and with some luck could technically achieve firepower or mobility kill against a tank or IFV. An updated design could surely prove a capable tool in the modern battlefield.

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    1. Again; vehicles with focus on indirect fires will hardly ever be sent into more risky duel (line of sight) combat situations voluntarily. Any "hybrid" nature of theirs is thus of little interest.
      Commanders of line of sight combat vehicles with a secondary indirect fire (NLOS) capability on the other hand would love to use a less risky indirect fires option at times, in assistance to other units or in preparation of LOS combat.

      The 2S1 is still promising for Third World armies and desperate Ukrainians. It may also work well in very swampy terrain in general due to the 2S1's characteristics. It's no good idea in EU/NATO, even if updated.

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