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In warfare, logistics are one of the most important aspects. Supply is arguably a more important factor than tactics and combat ability. Considering how important of an aspect it is, it is very valuable to know how many people are usually needed to support a marching army.

So, how many non-combatants are needed per combatant in order to support a marching army?

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  • $\begingroup$ Possible duplicate of Military Logistics: F' 'em and Feed them Beans! $\endgroup$ – James Feb 19 '17 at 3:53
  • $\begingroup$ The U.S. military can field about 100,000 ground troops in combat with about 1,600,000 active duty service members of whom about 500,000 are in the Army. There are about 1,000,000 civilians in the DOD, about 250,000 in the Dept of Veterans Affairs, and lots more in defense contractors both at home and in the field. $\endgroup$ – ohwilleke Feb 19 '17 at 20:31
  • $\begingroup$ @James I don't really think so, that question is asking for overall army size. I'm not asking about size at all but ratio of combat to support personnel $\endgroup$ – Miguel Bartelsman Feb 20 '17 at 3:49
  • $\begingroup$ @MiguelBartelsman If you read my answer to that question it is precisely what I provided as an answer. $\endgroup$ – James Feb 20 '17 at 15:02
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    $\begingroup$ I linked the wrong question via the mobile app this is the question I was thinking of as a duplicate: worldbuilding.stackexchange.com/questions/20826/… $\endgroup$ – James Feb 20 '17 at 20:18
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I found a very interesting document outlining the answer and I thought it's way too important of a resource not to share it

Ancient armies

Prior to 1000 B.C. armies were organized according to specific social structures. The nobles and members of the royal family rode in chariots. The cavalry was composed of lesser nobles and the infantry was made up of men from the poorest social classes. There was very little organization and no prearranged campaigns; battles were conducted similar to a modern day raid.

TTR in these armies was very low as nobles were expected to supply themselves and peasants were expected to live off the land.

Early military societies

Around 700 B.C., war became the main business of many nations. The need for increasing wealth was satisfied 40 mainly through the proceeds of armed combat. Military and political organizations began to consolidate and blend. Regular armies were created and the states, including their financial and administrative systems, were built around those armies. This military nature of the state extended well into the Roman Republic and even to the feudal era in the years 800 to 1000 A.D. A combination of civil and military authority on the general’s staff facilitated the administration and the logistics support of the armies.

Xerxes army is taken as an example. It is estimated that the size of the army was of 5 million and the fighting forces were around 150 thousand to 180 thousand. Even reducing the full figure by two-thirds (as contemporary writers were known for exaggerating numbers), TTR was around 9 to 1 (9 followers/supporters to 1 fighter).

The Macedonian army

The Macedonian Army between the years 350 to 320 B.C. was probably the best military force known to humanity up to that point and maybe even up to the 15th century when gunpowder weapons were introduced. For the first time in history, scientific analysis was used to design tactics and battle movements. Philip of Macedon developed the most thorough administrative and logistics system known and his son Alexander was the first to devise and use prototypes of field artillery that could be carried by mule or horse to the battle.

It is believed that the success of Alexander’s sustained military expeditions reflected in large part his careful logistics planning.

A study argues that the Macedonian Army employed one servant for every ten infantrymen and one for every cavalryman. Taking into account the infantry-cavalry ratio, as well as guards employed to protect camps, TTR results in an impressive 1 to 1.12 (100 followers for every 112 soldiers)

The Roman military system was based on an essentially professional citizen army. The Roman armies were successful because they introduced a new organization based upon age and experience rather than wealth or social condition. Rome traditionally had two consular armies, each consisting of 18,000 to 20,000 men. Each consular army was formed by two Roman and two allied legions, but in times of war there might have been more than the 8 standard legions. By 220 B.C. the total military manpower of Rome was calculated to be 750,000 men.

If the figures are to be believed, it would suggest that out of the 750,000 men about 710,000 were support personnel. Yielding a rough TTR estimate of 18 to 1. If garrison forces are excluded, the TTR lowers to about 10 to 1. Comparable to that of Xerxes but much higher than that of the Macedonian army.

Medieval armies

While figures to determine TTR in this era seem hard to come by, the french implemented in the 15th century the "Lance" system in order to support their troops.

Each lance consisted of a gendarme, a squire, 2 archers, and 2 pages or valets who served as foragers, scouts and pickets and were not counted as combatants

Resulting in a TTR of 1 to 2. Of course, when lances were grouped into big armies, it's very likely that the ratio increased.

Source: "An analysis of the tail to tooth ratio as a measure of operational readiness and military expenditure efficiency" by Tamara L. Campbell & Carlos H. Velasco

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    $\begingroup$ Regarding the Romans: they had more than eight legions. In the time of Caesar and Augustus, it was closer to 60, but this number was reduced by future emperors out of fears of military coups. Still, the number of legions floated in the 25-30 range for well over a hundred years. As each legion had roughly 5500 soldiers, that makes for a total count of around 150,000 to 165,000 soldiers (not counting the auxiliaries). Your source cites two consular armies, but fails to mention the legions on garrison duties (along the Rhine, out in the East, etc.) that were the greater part of Rome's manpower. $\endgroup$ – Palarran Feb 19 '17 at 3:36
  • $\begingroup$ For the number of legions, it specifically mentions that the period is 220 B.C. Of course, I don't know enough about the roman military to counterargue your point. $\endgroup$ – Miguel Bartelsman Feb 20 '17 at 13:19
  • $\begingroup$ I find the numbers for Xerxes hard to believe as they are so inconsistent with the rest of the data points and what would those 9 noncombatants be doing anyway? $\endgroup$ – Loren Pechtel Feb 21 '17 at 5:48

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