Loose cannon


A loose cannon refers to a cannon which gets dislocated and moves about randomly on the decks of a warship, creating a hazard to crew and equipment.
A famous literary depiction of a loose cannon appears in Victor Hugo's 1874 novel "Ninety-Three", whose plot is set during the French Revolution. In a well-known episode, a ship of anti-revolutionary French Royalists is sailing towards Brittany, to aid the anti-revolutionary Chouannerie rebellion. While at sea, a sailor fails to properly secure his cannon, which rolls out of control and damages the ship. The sailor risks his life to secure the cannon and save the ship. The Marquis de Lantenac, leader of the Royalists, awards the man a medal for his bravery and then executes him without trial for failing in his duty.
The widespread publication of Hugo's book, both in the original French and in translation to various other languages, helped make the concept of a loose cannon more well-known. It has eventually developed a metaphorical meaning relating to a person who is acting in a wild and unpredictable manner and who constitutes as much danger to his or her own side as to the enemy.