Henry's Disguise
The clearest example of dramatic irony in the play occurs when Henry dresses up as a common soldier in order to walk among his countrymen before the Battle of Agincourt. While the audience knows Henry's plan, the men remain unaware and as such speak candidly to Henry about the nature of war from their perspective, their opinions of the king, and their hopes for the battle to come.
French Defeat
In Act Four, the French forces are shown to lodge innumerable insults on the English. They are also arrogant and frivolous compared to the English camp's serious approach to the battle. The irony of the situation is that the audience is well aware that the French will soon suffer a major defeat at the hands of Henry and his army.
Traitors and Treason
Before Henry departs for the battle in France, he has royal commissions sent to Scrope, Gray, and Cambridge. While the three men think they are being given authority while Henry is away, Henry is actually revealing to them that he knows of their treasonous plot to depose him. Instead, Henry has all three men executed.
Henry's Games
While many characters comment in the beginning of the play about how thoroughly Henry has transformed from a mischievous youth to an effective king, Henry's actions toward the end of the play suggest that he has maintained some of his predilection for jests and disguise. When he dresses up as a common soldier, he displays some of the whimsical nature he exhibited in earlier plays (as "Hal"), but this time to aid himself and his men in battle.
