Martin van Creveld, Supplying War: Logistics from Wallerstein to Patton (Cambridge University Press: Cambridge, 2007) ISBN 0-521-21730-X
What John Keegan did to the experience of battle in 1979, Martin van Creveld did to the logistics of modern European warfare two years earlier. I finally read this book in May 2021 and am glad that I did, although its perspective is different than mine.
van Creveld lays out a model of logistics which goes like this. Before the late 19th century, armies could easily carry all the ammunition and spare weapons they needed with them, so the main requirements were food and fodder. As long as an army kept moving and was not too large, it could get these things in the area of operations. The main differences between armies were whether they confiscated supplies or purchased them, and whether they got their food from individual villages and farms, hired contractors to collect and deliver it, or obtained it from local towns and governors. So armies could wander around freely but might get in trouble if they had to stop to besiege a town or because enemies had blocked their path. If an army did not want to pay, then it was better to operate in hostile territory than friendly territory, just as Sun Tzu says. In 1870-1871, the Prussian army only consumed 56 rounds of rifle ammunition per infantryman and 199 rounds per gun (p. 102). This was less than the army carried with it when it set out, so there was no need to bring trains of ammunition from Prussia to the army. Outside of North Africa and some Pacific islands, the Axis still relied on local food and fodder in WW II.
Quite a few people interested in ancient warfare know an article by one F. Maurice on the water and roads at the Hellespont. After reading Herodotus’ story that Xerxes marched through the area with 1,700,000 infantry, 80,000 cavalry, and 20,000 charioteers and camel-riders and hiking around the countryside in summer, he argues that an army of 150,000 soldiers, 60,000 noncombatants, and 75,000 animals is the absolute maximum that could have been fed and watered in the area (paragraphs 10, 21, 33). I think this was the Major-General Sir Frederick Barton Maurice who was forced out of the British Army for political reasons in 1918, became a journalist and an advocate for veterans, and died on 1 May 1951. People cite it because he was an experienced staff officer who had walked the ground and talked to classicists like J.A.R. Munro. Its full of details such as that the British Expeditionary Force of 72,000 men, with railroads for supply but just horses for transport, needed 20 square miles for its camp in 1914 (the cavalry were stationed elsewhere and the motor vehicles had not yet arrived). But its certainly not the last say, and while he was talking to British classicists, a retired Bavarian general was preparing a study of the same problem and addressing their arguments.
One Robert von Fischer (d. 1937) commanded the 1st Royal Bavarian Landwehr Division in France from September 1914 to December 1915 and received the honorary title of Bavarian General of Infantry in 1917. He had similar military credentials as Maurice: he commanded a division on the Western Front for 16 months, Maurice served in the Tirah Expedition in Afghanistan, the Boer War, and briefly on the Western Front. And after examining the whole route and the problems involved, he felt that the Persian army was probably no more than 40,000 soldiers strong. Read more