The Battle of Agincourt on 25 October 1415 (St. Crispin's Day) resulted in an English victory over a larger French army. Henry V's victory ushered in a new period of warfare, in which Henry married the daughter of the French king and made his son heir to the French throne, but his achievement was squandered by his successors.
The battle is notable for its use of the English longbow, with the majority of English soldiers being archers, and is central to the plot of William Shakespeare's play Henry V.
Historians have drawn some inevitable comparisons between the modern era and Henry V's campaign in the 15th century. He landed at the mouth of the Seine on August 14 and began a tedious siege of the town of Harfleur at a time when France was on the verge of civil war between the Burgundians and the Armagnacs. The English king allied himself with the Burgundians, who, in today's terminology, became "local security forces" in Normandy.
Gradually he won the support of local merchants and priests, but at the same time all sorts of opponents of the English began to flock to the opposing camp. Basically the same as what was happening with "Al Qaeda" in Iraq.
The same thing happened to the English army in France during the Hundred Years' War, which ended with the Battle of Agincourt. It failed to control the continental territory and the battle of October 25, 1415. is probably its only notable victory.
What happened on the battlefield itself is well known - the English challenged the heavy French knights to march into a narrow muddy field, onto which their long-range bows poured cloud after cloud of arrows. At one point the French were so crowded that they could not raise their weapons, and those pushing from behind trampled the fallen. In the chaos and panic that ensued, the English organized a real massacre.
Regardless of the scale of the victory, the English ultimately lost because they did not keep their promise to restore order and peace among the French, and the civil war continued long after the death of Henry V in 1422.