Mines are some of the most dangerous weapons used on the battlefield. They are the unseen enemy that can totally wreck an army or a navy. While still destructive, land mines are often stuck in one place, easily found, removed, or bypassed once made aware of their presence. Naval mines have come a long way in a short time, and are able to count the number of enemy ships that pass before attacking and can even swarm oncoming warships.
How they take down warships starts with a bang.
A Polish Mina Morska naval mine used between 1908-1939.
The damage a ship takes depends on the power of the mine and its initial explosiveness versus how far away from the ship's hull the mine is when it explodes. The closer to the ship the mine is, the more direct damage the ship will take. But the direct damage isn't the only type of damage a mine does to a ship. Other types of damage occur from the bubble created by the underwater explosion as well as the resulting shock wave from the explosives themselves.
Direct damage can be exacted by using more and more high explosives in mines. This will also affect the bubble jet and shock wave. The bubble jet removes water from the area of the explosion temporarily, but when the water comes rushing back in under the surface, it does so at such high velocity that it can penetrate a ship's hull. The shock wave from a naval mine is enough to tear out the engines from a ship, toss around the crew, and kill divers.
Each kind of damage can do incredibly grievous harm to the ship and its crew. Results from mine detonations can be seen in incidents around the world. When the USS Samuel B. Roberts hit a mine, for example, the U.S. Navy stunned Iran with its response.
Read: The time the U.S. Navy unloaded on the Iranians in the most explosive surface battle since WWII
Modern mines are simple devices that are designed much like bombs. There is an explosive case surrounding an arming device and explosive train that will detonate the mine when it's supposed to go off. When mines are deployed, the arming device activates the mine. When the train is aligned with the arming device, the target detecting device activates. This is the trigger that senses when it should go off. There are many kinds of detection devices: magnetic, seismic, acoustic, and pressure mines.
Different kinds of ships generate a different response from different mines, and the mine is smart enough to know when to explode. When it does, the resulting explosion, bubble jet, and shock wave can literally tear a ship in two.