It took a while, but I finally grasped that the Ukraine case is a wonderful real-world anecdote to support my (much) earlier point about low force densities in modern ground warfare.
My point is that the distance between predominantly combat-seeking manoeuvre formations (such as a mechanised battalion battlegroup) would be very large in modern, European-style
I already mentioned at the link that even the Cold War setup was 26 divisions spread over about 1,000 km frontage (Central Europe). It's become much less since.
A decade ago or so even flag rank officers mused publicly about what it means to expect 100 km or more of gaps between two manoeuvre brigades. The Ukraine invasion scenario features this:
This graphic made the rounds a few weeks ago:
|(c) Dmitry Tymchuk|
A more detailed one followed recently:
|AFAIK (c) Washington Post, based on RUSI info|
The border in the Northeast and east of the Ukraine has a length of about 600-700 km*. The assembled forces of supposedly 80,000-92,000 men** are roughly the equivalent of eight to ten Western-style brigades. Now assume that at least in some places brigades would bunch up and you do indeed end up with gaps of about 100 km width.
This is very much the scenario I was discussing in 2012; a conflict without lengthy previous mobilisation or even arms racing.
It's not enough to keep the ~100 km gap under surveillance with a picket line. A picket line - especially if established by the not very combat-oriented modern armoured recce forces - may call in artillery fires on passers-by, but lacks the power to engage directly. 100 km gaps de facto exclude the use of unguided artillery fires on the middle of this gap. Helicopters cannot engage properly in face of capable battlefield air defences. Fixed wing air power is likely busy with air superiority, deep strike, main effort support or crisis management jobs. Even the A-10 fanbois got to admit that A-10's would likely be allocated to main effort support or crisis management rather than guarding the target-poor gaps.
So these gaps would not be defensible immediately. Hostile forces could push through suddenly. Mobile warfare ensues.
A corps commander doesn't need a mere picket line of observers, but rather area-covering (or at the very least bottleneck-covering) surveillance efforts - and preferably substantial delaying action capabilities in these gaps.
This is an area of military theory in which substantial improvements are possible over existing doctrines. This could be a golden age for armoured recce / cavalry - if only it develops along a wise route.
*: Border lengths depends on how you do the measuring - it's about 600 to 700 km if you simplify it into three lines.
**: It's ridiculous to call this a 'massing of forces' as so many "journalists" did since the troops are dispersed over a very large region.