"This story shall the good man teach his son;
And Crispin Crispian shall ne’er go by,
From this day to the ending of the world,
But we in it shall be remembered-
We few, we happy few, we band of brothers;
For he to-day that sheds his blood with me
Shall be my brother; be he ne’er so vile,
This day shall gentle his condition;
And gentlemen in England now-a-bed
Shall think themselves accurs’d they were not here,
And hold their manhoods cheap whiles any speaks
That fought with us upon Saint Crispin’s day."
Henry the V, William Shakespeare
The English expedition in France had been plagued with long wet marches, dysentery, and a French force determined to attack and capture/destroy them. When twenty-eight year old Henry the V's force of approximately 6000 moved towards the port of Calais to return to England he encountered a French force outnumbering him from 3-5 to 1. For the French it should have been an easy victory. The English force was nobles and commoners, many with the English longbow. The French had heavily armored cavalry, some crossbowmen, and legions of French noble knights.
The topography of the battlefield played well to the English. The flanks were heavily wooded, prohibited the cavalry from sweeping along the flanks to attack the bowmen. The field was wet and churned to mud easily. The land had difficult to see drop-offs which provided deceptive cover in the open too. Henry opted for a defensive fight, ordering his men to sharpen stakes and angle them towards the French position.
The French moved on the English first, sending their cavalry tearing at the English line, churning the field into a muddy ooze as they came. They encountered the English longbowmen, the machineguns of the medieval battlefield. With iron tipped bodkin arrowheads, these bows could rain down fire that could pierce the French armor - and did. The cavalry was devoured in raining waves of arrows.
The French crossbowmen moved forward to deal with the English bowmen. While effective, the crossbow took three times as long to load as the longbow. Soon these men were devastated under English bow fire.
The armored French knights slowly surged forward in dense formations, going over the muddy ground which slowed them considerably and made the trek even more difficult. The rain of arrow fire consumed them and the moving mass of men pushing forward often trampled the men ahead of them. The woods on the flanks served to funnel them into the English. The few knights that did reach the line found themselves dealing with the English knights who quickly finished them off or captured them.
The French sent a squad of knights to try and kill or capture Henry personally, only to have them cut to shreds in the process. A significant number of French knights were captured to be held for ransom, a common practice at the time. When Henry heard a rumor that French cavalry were moving to free the prisoners he ordered them killed so as to free up the men watching over them for battle.
In the end, the French force was decimated. Shakespeare did the rest - immortalizing the battle in his play Henry the V in the classic St. Crispin's Day speech.