Shakespeare was well aware of the use of the meaning of havoc and he used ‘cry havoc’ in several of his plays. The ‘cry havoc, and let slip the dogs of war’ form of the phrase is from his Julius Caesar, 1601. After Caesar’s murder Anthony regrets the course he has taken and predicts that war is sure to follow.

ANTONY:

Blood and destruction shall be so in use

And dreadful objects so familiar

That mothers shall but smile when they behold

Their infants quarter’d with the hands of war;

All pity choked with custom of fell deeds:

And Caesar’s spirit, ranging for revenge,

With Ate by his side come hot from hell,

Shall in these confines with a monarch’s voice

Cry ‘Havoc,’ and let slip the dogs of war;

That this foul deed shall smell above the earth

With carrion men, groaning for burial.