Aviation Week had an article about Boeing's project to mate the Small Diameter Bomb (SDB, original model) with the MLRS's solid fuel rocket in its 2012/10/22 issue.
This isn't the very first attempt to mate rocket artillery and bombs; the SDB was already considered (actually, 3 of them) as a payload of a cargo container version of the ATACMS missile system.
The blurring of the lines between artillery and close air support actually dates farther back; artillery guns were used in aircraft for ground attack purposes (not only gunships, but also several light and medium bombers of WW2 with 75 mm cannons such as Ju 88 and B-25).
The employment of aerial sensors for observation of artillery fires (such as forward air controllers or drones) blurs the differences as well; artillery is in theory capable to hit moving targets hundreds of kilometres away from friendly ground troops. Just as air power. Actually, this used to be one of the main justifications for costly air attacks.
The relationship of artillery and close air support (maybe even interdiction) as near-perfect substitutes appears to be largely established.
This fits well to the waning of air power's preference for bigger and fewer munitions than practical for the artillery. 50 kg bombs were small bombs by WW2, while at the same time a 42 kg shell was a heavy one for divisional artillery. Artillery largely gave up its relatively unwieldy heaviest (siege or long-range) artillery (beyond 155 mm calibre) during the Cold War and standardised quite close to the 42 kg shell mentioned before. Meanwhile air forces became to consider 227 kg bombs as "small" because dropping a huge munition is easier than lobbing one. This was largely responsible for the demise of heaviest artillery.
This trend towards bigger aerial munitions has reversed, with guidance allowing for many small munitions to score direct hits. The reduced power of the individual warhead is overcompensated b the directness of hit and the reduced probability of hitting someone (friendlies, civilians) or something you don't want to hit. Finally, the smaller munitions allow for lower payload carrier vehicles, such as modestly-sized drones. The BAT (sub)munition lead in this regard IIRC.
So in the end, artillery and air force munitions against ground targets can be technically identical or near-identical. Artillery prefers the long barrel howitzer for anything up to about 45 kg, and rocket launchers for bigger warheads. This preference is easily explained by the ease with which rockets allow the lobbing of very large payloads. You can move and launch an intercontinental ballistic missile with a dedicated truck. Guns on the other hand grow really big very quick.
|biggest railwaygun ever: 80 cm "Dora"|
It's best practice to choose between perfect substitutes based on price. Shall we?
Well, at this point the differences become highlighted:
Artillery either needs ground troops in the vicinity (which nowadays means within about 100 km radius) or it needs a rather inefficient method of propelling the warhead to the target (rockets).
Aircraft missions may cost ten thousands of Euros per flying hour, but a single 400 km-ranged missile is still more expensive than that.
Then again, you don't have such high peacetime operating costs with artillery. No training flying hours.
It's also rather unlikely that you will lose the launcher, and even if you do it might be worth less than the missile. Aircraft on the other hand have become so expensive that losing a single one is the equivalent of doubling of some city council's total debt. There's also -still- the crew's life at stake.
Artillery fires with non-nuclear warheads beyond more than about 500-1,500 km range are still most likely fiscally irresponsible compared to the ability to do the job with an aircraft. That is, IF you can do the latter. Few countries actually have this choice. For others, it's missile strike or no strike.
The Afghanistan nonsense has in my opinion delivered misleading indications. The availability of air power to the few ground forces outside of major forts has been luxurious, and the threat to air power has been negligible and thus not driven up the risk and expense. The biggest problem for air power was range and endurance of aircraft based outside of the theatre or logistics for aircraft based in the theatre instead.
I doubt that artillery will actually replace air/ground attack. The last years did nevertheless reinforce my opinion that the balance should shift between air power and artillery, especially between air power and missile artillery.
Air power could focus on versatile aircraft which wage their fight against hostile air power and hostile area air defences, while being able to be the digital eye for long-range missile artillery in between. Combat aircraft don't need to carry lots of ground attack munitions 'just in case' or be focused on one specific kind of ground target (with specialised munitions). They can instead be the sensor, and artillery delivers whatever is suitable at the moment. This could work at up to 300-500 km, depending on which missile system is being used. This could be the air interdiction of the future.
Meanwhile, artillery should be clearly preferred for close air support, or rather for support fires within 50-100 km of army formations (brigade or bigger). Classic, manned air power will probably vacate this niche entirely in the high-end fight, for drones are much superior in this realm - especially the 24/7 capability that stems from lower loss aversion.
Combat aircraft cannot maintain a patrol close to a hostile army brigade for long; such an undertaking requires much support to ward off the threats of fighters and surface-to-air missiles. Small and cheap drones on the other hand might be able to do exactly that; their loss is about as predictable and tolerable as the loss of munitions, and thus you need to spend much less effort to make their presence safe.
The combat aircraft of the future should probably no longer be described with munitions payload (the simplistic x,000 kg info on existing combat aircraft is mildly representative of actual wartime payloads for all but weapons bay-equipped aircraft anyway!). Instead, a description of the air/ground sensor suite and communications robustness should be much-appraised. Likewise, weapons bays should probably not be meant for ground attack munitions.
The 2009 blog post "TacAir of the future (?)" has already covered this to a large degree. I just wanted to reaffirm this.
Institutional inertia and inertia of perceptions will ensure that the change -if I'm kind of right- happens slowly, over time. Well, unless the shit hits the fan real big, for then everything happens in time lapse.
2011/02 Operational-level air warfare: Both the air force's and the army's perspective count
2009/11 TacAir of the future (?)
2009/05 Close air support
P.S.: I'm amazed the AviationWeek article is already on Scribd. That's not supposed to happen, I guess. Added the link to it.