2015/03/18

Battlefield missile artillery from the blackpowder age to the 21st century - Part III

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Rocket artillery was primarily an arm of destruction and killing during the Cold War. Signalling and illumination, even smoke-laying, had largely fallen out of favour. Mine scattering had been added, but this shared an important characteristic with the lethal warheads such as HE, VX, Sarin and DPICM: The dispersion of the individual rocket wasn't of much concern as long as the rocket salvo produced a nice cluster of impact points. Multiple rocket launchers were area effect weapons. Their area effect was often exaggerated, but small and low value point targets certainly had the wrong target profile for a MRL during the Cold War.



The rise of the PGMs

The Gulf War of 1991 that liberated Kuwait* was one of the events that ended the Cold War (by signalling that the West dared to withdraw forces from Germany to fight a war in the Middle East). It saw an unprecedented use of precision guided munitions (PGM) that actually mostly had their roots in the Vietnam War era (and of MLRS). The idea of 'smart' munitions as war-winning wonder weapons had grown during the 1980's ("assault breaker") during belated desperate attempts to find a counter to Warsaw Pact numerical strengths, and this idea grew very much after the demonstration of such munitions' capabilities under the mostly very generous geographical and meteorological conditions of the Mid East.
There were dozens (mostly not loudly marketed) development programs for guided mortar munitions by the late 1990's, and likely even more for rocket artillery. Gun artillery on the other hand had a hard time since the typical 155 or 152 mm howitzer shell is spinning very quickly and thus difficult to steer.

Some of the cheaper concepts for rocket artillery PGMs did not employ a full steering, but merely a correction of the range error, comparable to the AZON guided bomb of 1944. Such schemes require no fins; it's enough to simply deploy some kind of air brake at the correct time - and the calculation of the correct timing is possible with radar or optical tracking of the rocket in flight (or with INS, SatNav). This works well for spin-stabilized projectiles, too.

A typical howitzer shell dispersion pattern; similar for MRL fires
It's also possible to remote-control rockets in flight based on radar tracking.

Multiple rocket launchers often have a horrible dispersion
beyond 2/3 of their maximum range.


More ambitious 'smart' rocket artillery tends to employ satellite navigation (with INS backup) and fin steering. Both satellite navigation and inertial navigation systems have been miniaturized to chip size and less than 100 grams mass, and hardened against the accelerations even of howitzer shots.
Precision guided submunitions such as Bazalt Motiv-3M (for 300 mm BM30) or 9M55K1 (for 122 mm BM-21) are rare, expensive and specialized munitions for anti-tank tasks.
Anti-radar artillery rockets are even more rare.

To be honest, rocket PGMs are a rather uninteresting topic by now since the principle is well-known and actually quite simple.There was so much attention on guided artillery rocket programs in the past that it's a thoroughly worn-out topic.

The reduction of dispersion to enable rocket artillery against point targets was matched by an improvement of the launcher system's positioning. Satellite navigation, digital northfinding and digital maps reduced the battery from a tactical to an administrative unit. The launchers of a modern MRL battery could be employed separately since the all can determine their position and orientation quickly and reliably. This was previously a battery-level effort. 1980's-style counterfire to such dispersed MRLs would be very inefficient since multiple MRLs would shoot for the chance to disable but one instead of six MRLs. Dispersion of launchers coupled with "shoot & scoot" tactics (leaving the site of the last salvo within less than 2 minutes and driving to another site to be ready for the next salvo as soon as possible) created huge area management troubles in face of the lingering counterfire threat: A single artillery regiment could fire from hundreds of different locations during a day, and these locations would be under risk of counterfires for extended periods thereafter. Furthermore, the artillery coordinator needs to avoid patterns in the choice of firing locations to prevent predictability.

Modern surveillance technologies add to the troubles: The Cold War vintage artillery radars could calculate the origin of rocket in the air (unless they manoeuvred much, another advantage of PGMs). Radar surveillance systems such as E-8, ASTOR or the decommissioned French Orchidée can conduct a spot search at these places and possibly even identify and track the MRL on its move until it comes to a halt. Finally, artillery counterfire might hit that new location instead of the old firing location. A resupply truck might be caught as well. The MRL would still be a point target even in company of a resupply truck, so a guided rocket might be the best choice to engage it. Howitzer artillery would rarely be available since it can barely exceed 40 km range, which even 122 mm rocket can exceed nowadays.

The lingering threat of counterfire and the inherent dispensability of great launcher accuracy if GPS-guided rockets raises a question about the nature of the MRL: Why not go back to launching from cheap trailers or even the transport package rested on the ground in a ~45° angle, as did German rocket artillery during the Second World War? An extreme example of this approach was "Netfires", essentially standing containers which launched PGM rockets vertically and turned out to be prohibitively expensive (because the U.S.Army 'managed' their development).

Gudmundsson's book "On Artillery" appeared in 1993 and had an outlook into the future as its closing chapter. Gudmundsson was very much under impression of the fibre-optic guidance principle, which enables to user to 'see' the target with the missile's 'eye'. The Polyphem missile project embodied this and the project started in the following year, but was cancelled after a decade. Actually, all fibre-optic guidance projects for mortars and artillery were cancelled or didn't reach operational capability yet as far as I know. The technology succeeded in anti-tank missiles only. Gudmundsson's vision of artillery overcoming the separation between itself and its targets by firing artillerymen being able to see their targets again did not come true so far. The division between the observing artillery and the firing artillery persists.

The cluster munitions ban

The cluster munitions ban of 2008 (previously discussed here, Russia and the USA did not join it) bans most DPICM munitions, and for a good reason: Dud rates of at times 10% added a secondary "anti-personnel" (anti-humans, anti-livestock etc.) minefield function to every DPICM shot. This had been true with very early cluster munitions such as cluster bombs of early WW2 already. It is possible to minimize the dud rate or make duds harmless (such as with charged capacitor-dependent fuzes), but efforts to develop and introduce such came too late.

The challenge was thus to develop alternatives to the extremely large area fragmentation effect of individual DPICM rounds - something better than mere HE, even HE with air burst.
One approach was the cannister/flechette principle of many, many tiny steel arrows packaged into the warhead and released in time so they would impact with an optimum mean distance between each other. I'm serious, some arms companies are actively marketing this. This was not introduced apparently. It wouldn't help much anyway, since flechettes have a horrible and exaggerated reputation as well.

Another approach was practised by the Russians even before the ban: HE submunitions were ejected from the rocket and sank on individual parachutes to the ground for an air burst with an optimum pattern of fragmentation. This makes sense because a HE rocket impacting at a very shallow angle would send most of its fragments either into the ground or up in the air, hardly any forward and none backwards. Left and right side would be pierced by a tiny fraction of the overall fragments only. A HE submunition descending vertically and exploding at optimum height over ground would affect the ground below by blast and all of its fragments would go left, right, forward, backward - hardly any would be wasted.

9M53F rocket principle: separable, parachute-retarded HE warheads
This may work within the limits of the treaty for MRLs, but makes little sense for guns. The ban would forbid more than one such submunition, and howitzers can control the angle of descent fairly well with the choice of propellant charges and barrel elevation. Rocket artillery cannot control its angle of descent nearly as well; the only option is to add drag rings to the rocket's nose for a choice of only two angles of descent for a given range, and such rings are unavailable for MLRS due to its packaging concept AFAIK.

Another possible future for rocket artillery is a return to unitary (HE) warheads, especially if coupled with PGM characteristics. The GUMLRS missile is a prominent example. The physics that led to the employment of ICMs do still apply, though: The fragmentation effect per kg of mass is higher with smaller warheads than larger ones. The 122 mm calibre looked obsolete during the 1980's, but it's better suited for HE warheads than 227 mm rockets as used by MLRS. You'll be able to cover a larger area with HE fragmentation per truckload of munition. Guided missiles don't need the large HE warhead of a GUMLRS either, which is why many of the recent MRL guided rocket developments used much smaller calibres. MLRS can be adapted to such smaller calibre rockets, of course; even the original mine scattering rockets deviated from the 227 mm calibre of the M26 rocket already. A 122 mm launcher pod that fits into MLRS systems can hold 28 122 mm rockets.

later: Part IV - Options for the (near) future of rocket artillery

S O

edit 2015-11: Corrected the part about the Russian concept.

*: By handing it over to absolutist monarch whose clan was and is the embodiment of a kleptocracy.
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