The term, loose cannon, has been around a long time. Cannons used on sailing vessels were large, typically weighing several tons. To avoid damage from the recoil when they were fired, they were mounted on rollers and secured with rope. The cannon jumped backwards when fired. If you have ever fired a weapon, you are familiar with recoil. The cannons get hot when they are used in battle, and each time a cannon is fired, it jumps higher and rolls farther. If the ropes holding the cannon secure were to break, a loose cannon would roll backwards and crush anything—or . . . → Read More: Loose Cannon on Deck