HISTORICAL EXAMPLE: LOGISTICS OF THE XERXES INVASION OF GREECE 480-479 BCE

Greece was a poor country incapable of supporting invasion forces, so when Persian King Xerxes invaded Greece in 480 BCE to establish an ethnic frontier in the west of his empire, he had to rely on external resupply to support his 150,000 infantry, 30,000 cavalry and 600 warships with 120,000 crewmen. The distances were such that wagons would have their load consumed in transit by the draught animals, so supply had necessarily to be by sea.

The Persian war fleet was superior to the Greek one, so it provided both outflanking amphibious capability and protection for the resupply fleet; the amphibious capability meant the Greek forces could not concentrate, remaining at home defending their cities, and so able to be picked off one by one. The Greek strategy was to neutralise this war fleet, both to even up the operational mobility equation and, by depriving the Persians of supply, ultimately force their withdrawal.

Given the inequality of the fleets, the Greeks determined to force sea engagements in narrow waters to minimise the effect of the opposing superior ships and numbers: they closed the land route to the south at the Thermopylai pass to force a Persian outflanking amphibious operation in the adjacent strait. When three days of naval engagements failed to give a Greek victory, and the Thermopylai position was outflanked on land, the fleet withdrew to the strait between Salamis and Athens, and by a stratagem of splitting the Persian fleet, defeated their naval force and so exposed the sea supply line to naval interdiction.

With no resupply, Xerxes was obliged to take half his army back to Asia Minor and the remaining part had to withdraw and winter in the plains of northern Greece to survive. The following spring, the southern Greek states, no longer threatened by enemy amphibious landings, were able to concentrate in full strength at Plataia and defeat the reduced Persian army and its Greek allies. In parallel, the Greek naval forces captured the rump of the Persian fleet at Mykale in Asia Minor.

Afternote:
Invading Persia 150 years later, Alexander had to attack across central Asia without the option of water transport. His campaigns were carefully timed to coincide with the ripening of crops, as land transport could not possibly keep up the food and forage for his forces.