Red Army = most effective force !

[narwan]

Marcello said:
Which requires digging hundreds of meters or kilometers of deep trenches.

No it doesn't. It is a common misconception that in order to significantly disrupt a supply network you need to take out every link. You don't. You only have to take out one (the weakest being the easiest target).
The capacity of a supply system is determined by the lowest capacity point along the entire chain. For example, if you have two long stretches or road of equal width, length, material, incline etc. The only difference is that one of them has an extremely sharp bend halfway. That one will have a lower capacity for the simple reason that traffic will need to slow down in order to make the turn. It doesn't matter that all the miles before and after the bend it has the same capacity as the other road. It's the choke point (the bend) that determines the capacity of the entire line. Does that mean that taking out one point suffices to make a supply chain collapse (temporarily)? Sometimes it does. A lot of WP division would be moving over very few roads in the northern sector. That means they can't easily switch roads for supply chains without disrupting each others supply. So one bridge taken out along a supply route can halt the flow along that entire supply chain. Until it's replaced. By an engineer bridge which will have a much lower capacity and which in turn can be taken out again.
Besides the capacity of a network there's the question of the absolute time which it takes for one specific unit of supply to cross the whole chain. The road example again; if you add some more curves and bends after the first one which are not as sharp you won't add a 'weaker' link than there already is. Those additional bends will cause each vehicle to slow down somewhat though again adding to the time for that vehicle (and it's load) to get to its destination. So each additional weakening of links will reduce the capacity of the part from the previous (and weaker) link.
Delaying is the whole point of obstacles and blockages. Going around them may look like a TACTICAL solution, strategically it doesn't solve the problem of being delayed. It takes time to go around, especially in war with all its uncertainties (and certainties...).

Think of the emergency exit of a public building. If it doesn't have the capacity to let through everyone on time casualties will occur. Not just because of the emergency itself (a fire for example) but also because of the crowding in front of the exit (in supply terms it means that traffic jams will happen in front of choke points and those jams themselves will reduce the capacity further). Now imagine that exit being closed (a bridge blown up or other weak link taken out). Someone can go around with a key and open it from the outside but not only will additional casualties have occurred (and huge traffic jams created) it may very well be too late all together. The door needs to be open at exactly the time you need it. Not five minutes later. Same with supply.
Logistics is NOT a simple and easy affair which tags along the combat elements. It governs the combat elements. And it is very susceptible to disruption.

Narwan