The short version is that they allow:
(a). Packet level logistics/supply-chains (packet switched supply-chains vs circuit switched). This is already true, but autocars would allow fine-grained routing.
(b). On demand (JIT) supply chain and automated weapon rental (set an auction for the water or vehicle support you need in 8 hours let the invisible hand of the whuffie[2] market solve it). Command and Control is no longer a command economy, replaced with Auction and Effect.
(c). Really slow cruise missiles that are indistinguishable from SUVs because they are SUVs.
(d). Autocars make nice surveillance and CCC platforms as well.
Outside of Freedom_tm, the US military wants an autocar so that it doesn't have to worry about soldiers/contractors dying to bring supplies between military bases during an insurgency (see Iraq, Afghanistan).
A military that used autocars for logistics would greatly reduce the number of soldiers in support roles. This would in turn reduce the resources necessary to sustain combat forces which would again reduce the resources used. Think the Propellant Mass Fraction[3] applied to war logistics. With automated supply chains, armies flip from 80% support 20% combat forces to 80% combat forces. As logistics becomes easy, so do empires. Nations can utilize recruits more efficiently so you need a smaller population base. Occupation of other nations costs less in terms of your resources and lives. It shifts the balance of power away from traditional guerrilla warfare. A second age of empire building (I don't think this is a good thing). Only those with Nukes are safe from the new empires.
The Roman empire was built on its roads. Napoleon's greatest weapon was his lack of a supply chain (he had a JIT supply acquisition process). Alter the efficiency of logistics and you change everything.
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