I added this map to my previous post on the Russian invasion of Ukraine, and it is worth studying. War in Ukraine has to be supplied by rail. One reason why many people much more knowledgeable than me did not believe Putin would actually invade was that the Russians had plenty of tanks and aircraft but not the trucks they would need to supply such an attack:
logistically, Russian forces are tied to railroad from factory to army depot and to combined arms army and, where possible, to the division/brigade level. No other European nation uses railroads to the extent that the Russian army does. …The Russian army does not have enough trucks to meet its logistic requirement more than 90 miles (140 km) beyond supply dumps. To reach a 180-mile (290 km) range, the Russian army would have to double truck allocation to 400 trucks for each of the material-technical support brigades. To gain familiarity with Russian logistic requirements and lift resources, a useful starting point is the Russian combined arms army. They all have different force structures, but on paper, each combined army is assigned a material-technical support brigade. Each material-technical support brigade has two truck battalions with a total of 150 general cargo trucks with 50 trailers and 260 specialized trucks per brigade. The Russian army makes heavy use of tube and rocket artillery fire, and rocket ammunition is very bulky. Although each army is different, there are usually 56 to 90 multiple launch rocket system launchers in an army. Replenishing each launcher takes up the entire bed of the truck. If the combined arms army fired a single volley, it would require 56 to 90 trucks just to replenish rocket ammunition. That is about a half of a dry cargo truck force in the material-technical support brigade just to replace one volley of rockets. There is also between six to nine tube artillery battalions, nine air defense artillery battalions, 12 mechanized and recon battalions, three to five tank battalions, mortars, anti-tank missiles, and small arms ammunition — not to mention, food, engineering, medical supplies, and so on.Alex Vershinin, “Feeding the Bear: A Closer Look at Russian Army Logistics and the Fait Accompli,” War on the Rocks, 23 November 2021 https://warontherocks.com/2021/11/feeding-the-bear-a-closer-look-at-russian-army-logistics/
Such an army also needs massive stockpiles of gravel, culvert sections, asphalt, concrete, and other materials to repair roads and bridges. Just driving heavy armoured vehicles damages roads, especially during the rasputisa. When vehicles burn out on the roads, they damage them more. Prepared defenders demolish bridges, block roads, sink boats in waterways, and launch bombs and missiles at any transport infrastructure the invaders build or capture. If you overlay a scale on maps of Ukraine, you can see that most of the Russian advances have not gone beyond this 90 mile / 140 km rule of thumb. The USA is so rich that it could supply the war in Afghanistan by truck from Pakistan (Afghanistan has no railways). Russia is not so rich, and its army is built around railways.
With a glance at the first map, you can see why it was so important for the Russians to take Kherson at the mouth of the Dniepr River (the river which divides Ukraine into eastern and western halves). It is a rail junction so lets them bring up supplies from Crimea for attacks further west. Zaporizhzhia is not just the site of a nuclear power plant but the next city along one of the few rail lines the invaders control. As we saw in my review of Supplying War (link), modern armies consume ammunition, spare parts, fuel, and all kinds of things which have to be made in distant factories and brought to the fighting. Ransacking supermarkets and draining gas stations only goes so far. And it is much more expensive to transport those things by truck than by rail, and even on paper Russia has a small transport fleet for its fighting force. Just like in the Iraq war, local militias are concentrating their attacks on transport because its much easier to fight a column of trucks than a column of tanks. And on 13 or 14 March, the Ukrainian armed forces announced the destruction or capture of a column of 200 vehicles near Melitopol.
As of 14 March, both Kyiv on the Dniepr and Kharkov on the Russian border appear to have multiple intact rail connections to free Ukraine. Refugees can escape along them and weapons, ammunition, food, and fuel can come in. So do the Ukrainian troops facing the Russian proxy states on the Don River in the east. The Russian advance along the Sea of Azov towards Mariupol seems to have followed roads, not a railway (this may be one reason why they are blockading the town but not assaulting it). And the Ukrainians claim to have destroyed 200 Russian vehicles and a headquarters near the railhead at Melitopol on 13 March, so a large Ukrainian unit seems to still be in the area. The Russian army would like to trap part of the Ukrainian army in a Kessel against the proxy states on the Don or force it into a massed retreat where Russian bombs and missiles can hit it in the open. But so far, the Ukrainians have been successful in keeping their railroads running and preventing the Russians from advancing along the rail lines. The longer that they can continue, the colder and hungrier the Russians will get (and the harder it will be to keep bombarding Kyiv).
Edit: I am also seeing claims that the Ukrainian Territorial Defense have been moving around in unmarked cars, while the Ukrainians show photos of a Russian ambulance full of munitions instead of wounded. The need to move but not die is driving this war in uglier and uglier directions (if any civilian car could be full of militia, Russian troops will shoot cars that don’t stop on command; if a marked ambulance could be full of munitions, Ukrainians will target them).
Edit 2022-03-16: added a map with the ’90 mile limit’ and Russian advances marked
Edit 2022-03-25: I am seeing claims that Russian logistics are not even based on cranes on the trucks lifting pallets onto the truckbeds and that many shippers inside Russia do not use containers https://nitter.eu/TrentTelenko/status/1507056020656427008#m This is madness.