The Physics of Medieval Archery describes the role of the longbow on the field of battle at Agincourt -- that "we few, we happy few, we band of brothers" battle fought between the English, under Henry V, and the French on October 24, 1415:
Henry had approximately 5,000 archers at Agincourt, and a stock of about 400,000 arrows. Each archer could shoot about ten arrows a minute, so the army only had enough ammunition for about eight minutes of shooting at maximum fire power. However, this fire power would have been devastating. Fifty thousand arrows a minute - over 800 a second - would have hissed down on the French cavalry, killing hundreds of men a minute and wounding many more. The function of a company of medieval archers seems to have been equivalent to that of a machine-gunner, so in modern terms we can imagine Agincourt as a battle between old-fashioned cavalry, supported by a few snipers (crossbow-men) on the French side, against a much smaller army equipped with machine guns. Perhaps from this point of view the most remarkable fact about the battle is that the French ignored the very great military advantages of the longbow.
One point the article doesn't mention is the effect this would have had on the horses. Whether the rider was injured or not, if an arrow struck his mount, he would be unhorsed and at a great disadvantage in armor designed for cavalry, not infantry. Once the riders were stumbling around on the muddy ground in their pointy metal shoes, the archers, now out of arrows, surged forward with daggers and lead mallets used for driving tent spikes. They worked in pairs, with one coming up behind a struggling or injured knight and felling him with a mallet blow and the other lifting up the visor and finishing him off with a dagger. If you want to read a truly brilliant account of this battle -- including a memorable explanation of why you never want to know what knights in armor smelled like -- you can't go wrong with The Face of Battle by John Keegan.