During the Hundred Years War, the French were defeated by the English(and Welsh) Longbowmen time and again. Each time they set their horses to the gallop, they charged into a storm of arrows which slaughtered them.
One particular french Duke came up with a plan which involved exhausting the archers’ arrow (ammunition) supplies. He studied the English tactics and the supply of arrows the individual archer would carry. He came to the conclusion that if one sent in the worst troops first, and kept pushing them forward, eventually, the archers would run out of arrows. At which point one would send in the knights and finish them off.
So, one day, in Britanny, he hears of an English wagon train moving from one castle to another and being escorted by a column of 250 mounted-archers (read mounted-infantry). So, off he sets with approximately 6000 men, to attack them. He puts his plan into action and sends in his poorest troops, which are anihlated. Following them are his Men-at-arms, which are of a better quality. They too are decimated. Finally, he sends in his knights. The English bowmen stand their ground and decimate the knights also.
So, why did the plan go so drastically wrong?
The wagons were loaded with supplies of arrows which were being distributed among the English castles.