I looked up something that I wanted to use for a footnote in my book (found it) and stumbled on this:
[...] one artillery battalion  that served in the Gulf War  had a basic load of 5,690 shells. Of them only 599 were standard high explosive (HE) , with another 307 rocket-assisted HE (intended for long-range missions). In other words, less than 16 percent of the basic load was usable in close supporting fires. Almost 60 percent was DPICM, while another 21 percent was scatterable mines, most often used by brigades and higher-level organizations. The remaining were white phosphorus (3 percent), illumination (less than 1 percent) and Copperhead laser-guided antitank rounds (less than 1 percent). With so few high-explosive and smoke rounds, the artillery clearly has a different focus from small-unit fire support .
"The Art of Maneuver", Robert R. Leonhard, 1991, p.287
: M109A5 self-propelled howitzers, calibre 155 mm
: of 1991
: about 24 km range
: about 30 km range, increased dispersion
: This is why.; add some dispersion to the graph to imagine the actual minimum safe distance. It's about 300 m with HE if the army is not obsessive about avoiding accidents.
|Some mil porn to keep readers awake and from closing the tab|
The figures are a bit uncommon, for this kind of stuff is rarely published, and I think it's thus worthy of repetition. The ratios are certainly obsolete, and totally off for those armies which are subject to the cluster munitions ban. Consider it a bit of info about the U.S.Army of 20 years ago.
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Leonhard's stance back in that '91 book (in which he was a 3GW guy, as opposed to being a RMA guy in his later book - a very confusing career) was to complain about counter-artillery focus and about lacking support of manoeuvre units.
He overshoots the target a bit by writing "small-unit fire support" (my emphasis) at the end*, for as a maneuvrist he should have understood that arty is not meant to support small units in general. That's what mortars are for. Arty is meant to be the formation commander's ultra-quick Schwerpunkt weapon. Arty can move its effect around on a map much quicker than tanks can move, and it can do so without signalling the location of its focus in advance. Arty can first support a deception move ad then switch all its firepower to support the main effort.
Leonhard wrote this inaccuracy into his book before small wars became all the rage and individual platoons once again began to receive fire support greater than what almost all WW2 infantry regiments could have expected.
I remember a complaint in some 80's or 90's literature about a Vietnam-era tactical vignette, in which an infantry captain was meant to practice how to allocate multiple mortars, artillery fire missions and even strike aircraft support for his company's fight. Back then, small forces received disproportionate fire support and many people's idea of what skilled company leadership looks like became warped into the image of a super-forward observer.
I suppose we're partially back to that point, as many veterans from Afghanistan have become accustomed to a degree of attention by higher level support that would simply not be available in a war against a real threat (a "peer vs peer conflict") or any other kind of conflict with many forces engaged in fighting simultaneously (the infantry captain from the Vietnam War scenario would almost certainly not have had such support during the simultaneous engagements of the Tet offensive).
I wrote this because the idea that close air support and artillery support ought to be always available for infantry or mechanised forces in combat is on a high tide, and it's simply not a good idea. Sure, it's a nice to have, but it will very often simply not be available, and this means infantry and mechanised forces need to be effective without. It would often times be outright wrong to distribute higher level support that much, it's higher level commander's responsibility to prioritise and assign his assets accordingly.
This is in part the case for 120 mm mortar support organic to manoeuvre groups**, something that has atrophied in Germany a lot. Even the new army structure adds only token 120 mm mortar support to entire manoeuvre brigades (in the added infantry battalions).
link: slightly related article of mine about arty
*: squad, platoon
**: Battalion-sized battlegroup to small brigade.
edit: I forgot to mention that there's an exception. Troops (hardly small units other than forward observer teams) far away from a Schwerpunkt might be extra reinforced by artillery fires in order to save line-of-sight combat troops (economy of force)..