Naval mine
Naval mines were explosive weapons used by the Continental Army during the American Revolutionary War, when facing the overwhelming naval force of the British Army.
Commonly, naval mines were set up in harbor regions to act as deterrents, and to impede land invasion by sea. They were designed to sink ships or other seaborne craft, or as a threat to prevent the usage of an area of water. Moored mines were tethered to sinkers, and floated at predetermined depths.
The firing mechanisms of mines were either traditional pressure points, which detonated the explosive on contact. However, some harbor mines were controlled by a pressure plate at its top, which could be turned off to allow transit of friendly ships.
These mines, however could be destroyed using cannon shots.
Origin
Naval mines originated in the 16th century, but their use in naval combat began in the American Revolutionary War. Such mines were created by David Bushnell, who placed the devices under or near the hulls of British ships in New York's harbor, by using a small wooden submarine he had invented called the Turtle.
Gallery
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Concept art of Aquila steering through naval mines
Reference