The mercy that was quick in us but late
By your own counsel is suppressed and killed.
You must not dare, for shame, to talk of mercy,
For your own reasons turn into your bosoms
As dogs upon their masters, worrying you.—
See you, my princes and my noble peers,
These English monsters.
(Act 2, scene 2, lines 85–91)

With these lines, Henry opens a long, moralizing speech in which he orders the execution of three traitors charged with plotting his assassination: his former friend, Lord Scroop; his cousin, the Earl of Cambridge; and a nobleman named Sir Thomas Grey. Despite his close relationships with two of these men, Henry knows he must set his personal feelings aside and uphold the law of the land. Henry therefore addresses these men as “English monsters” and, with a seemingly cold sense of ruthlessness, sends them to their deaths. We in the audience will remember this scene at similar moments later in the play, such as when he exhibits an unflinching coolness upon hearing that his old friend, Bardolph, is scheduled to be hanged.

                    Therefore, you men of Harfleur,
Take pity of your town and of your people. . . .
If not, why, in a moment look to see
The blind and bloody soldier with foul hand
Desire the locks of your shrill-shrieking daughters,
Your fathers taken by the silver beards
And their most reverend heads dashed to the walls,
Your naked infants spitted upon pikes
Whiles the mad mothers with their howls confused
Do break the clouds, as did the wives of Jewry
At Herod’s bloody-hunting slaughtermen.
What say you?
(Act 3, scene 3, lines 27–42)

Prior to invading Harfleur, Henry issues this blood-curdling threat to the town’s governor, explaining what his soldiers will do if his hand is forced and the English army invades. The vision of physical and sexual violence he unfolds here is shocking, but his threat is likely a bluff and hence just another example of a perfectly calibrated political performance. After all, the governor quickly relents and allows the English to take the town without additional bloodshed. However, had he been pressed to do so, Henry likely would have made good on his word, suggesting a willingness to be ruthless if and when the situation demands it.

                            I blame you not,
For, hearing this, I must perforce compound
With my full eyes, or they will issue too. [Alarum.]
But hark, what new alarum is this same?
The French have reinforced their scattered men.
Then every soldier kill his prisoners.
Give the word through.
(Act 4, scene 6, lines 33–39)

Henry addresses these lines to his uncle, the Duke of Exeter, who has just brought himself to tears while recounting the deaths of two noblemen during the Battle of Agincourt. Henry acknowledges the sadness of the account and feels moved to tears himself. However, when an alarm sounds, he quickly suppresses his personal sadness and reverts to his kingly responsibility. Looking out on the battlefield, he sees that the French army, which had formerly been scattered, has now reassembled into fighting formation. Sensing that this is a decisive moment in the battle, he makes a decision that, though ruthless, demonstrates an agile and strategic military mind: he calls for the merciless execution of all Frenchmen held prisoner by the English.