In simple terms it is” how many men are required to support one fighting soldier.”
The lower the number of tail the better it is for the budget of the army.
To support a fighting force you have Ordnance Corps to supply and replenish Arms and Ammunition.
In addition you have an Army Supply Corps which gives you food, vehicles to move and other provisions like Water,Petrol and cooking staff.
Electrical and Mechanical Engineers to maintain your equipment in war and peace.
Engineers to go alongside to make bridges, bunkers and other support to fight.
Army Medical Corps to look after your health and causalities.
Computers have made life easier but physical movement and storage of equipment has to be done on as required basis.
It is a mammoth task to maintain an Army and a herculean task to move and feed it during war.