(10-02-2022, 04:49 PM)BostonCard Wrote: I’m probably revealing my ignorance here, but is defending “more territory” the right metric? Area of territory defended is meaningless, or Russia would be in big trouble having to nominally defend the largest country on the planet. But Russia doesn’t really have to defend Siberia, or even the border with Finland (and there are reports that it isn’t). So, really, it is a question of the line of defense, right? I suppose that now that Ukraine has extended its control in Karkiv to the border with Russia, it does have to worry about Russia attacking from Belgorod or Belarus again, but it took Russia months to set up an attacking force from there, so I presume Ukraine will know if it is threatened again. So, as Russia retreats to consolidate its own vulnerable lines, that also reduces the breadth of the lines for Ukraine. I think under that logic, the advantage that Russia gets is that it can concentrate its forces so it will be harder for Ukraine to push further, but I don’t think it means that Ukraine will have a harder time defending its territory once it is consolidated. What am I missing?
BC
Area doesn't matter as much as the length of the line of contact. If the line of contact becomes longer you generally need more troops. In an "ideal" situation, the defender doesn't need to garrison the line of contact. The defender distributes his forces in depth near transportation hubs and "important" points in the defended area. The defender doesn't want to concentrate too much because it is easier for the opponent to damage the concentrated force. Distributed forces are harder to damage.
The defender then moves the necessary forces from their locations to counter attempts by the enemy to cross the line of contact. Sounds good, and it can work. However, there are problems. If the enemy can damage the lines of communication by air, artillery, or special forces, the defenders may not get there in time. Obviously, if the attacker can threaten multiple attacking axis simultaneously, the defender has to move forces to multiple places. The defender may not have adequate forces or adequate knowledge about the attackers real intentions. These are all serious problems.
Worse problems arise when the political and economic considerations of the country are added to the mix. There may be many points near the line of contact that are heavily populated or critically important to the economy. The attacker cannot be allowed to "harm" these points even temporarily. They must be defended "forward". This constrains the defender to garrison these points. It may also be necessary to prevent the attacker from moving freely inside the defended area because the attacker can threaten multiple critical points simultaneously that can't support each other if attacked. These points too must be defended "forward". The more area you hold the more of these points you have. It spreads you out and makes you strong nowhere.
It is also necessary to occupy the line of contact to at least the point you can observe and monitor your enemy. At times it may be advisable to build either field or permanent fortifications to deter/slow down your enemy. If you do this, you must overwatch the obstacles or they are useless. This eats troops too and is the ultimate example of a "forward" defense. Hard though it may seem to believe today, the argument about a "forward" vs a reactive defense in depth was a MAJOR point of contention in NATO during the cold war. As Germany became stronger and more important in NATO, the idea of not defending Germany "forward" became a political minefield. Defending "forward" was not popular with the US and the UK military.
Ukraine suffers from not having a heavily mechanized force that is well trained and can move rapidly from one area to another and fight on arrival. In theory, Russia could do that, but in practice they have not been able to do that. The forces of the DPR and LPR are even less mobile than Ukraine. As a result both sides are vulnerable to a concentration of force by the attacker. Russia has just shown us a textbook example of "he who defends everywhere defends nowhere", but as their slow attempts to move forces to reinforce Lyman and Izyum show, they are also incapable of a "mobile defense in depth". They also had no prepared rally point that the forces being attacked could break contact and retreat to.
Ukraine has shown the ability to concentrate a striking force and use it. Russia has not. Their attacks in the beginning of the war were "setpieces" against an enemy that wasn't fully prepared. Russia's advances in the Donbas, while very real and very destructive, were artillery driven. They simply fired until the defenders had to give way. Ukraine never suffered an encirclement or a "loss of control". They gave ground, they lost battles, but they never lost cohesion. Russia has lost cohesion a couple of times recently.
The fear is that Ukraine will be spread out in the areas they have returned to their control, and therefore will be vulnerable in the same way Russia was. If Russia can execute an offensive as effectively as Ukraine just did, the fear will be real. So far, Russia hasn't been able to do such a thing.