May 24, 2025: Russia, long an enthusiastic user of naval mines, is now on the receiving end of such devices. Since late 2024 a growing number of Russian ships in the Black and Baltic Seas have been damaged by limpet mines placed on the hulls of Russian oil tankers. At least half a dozen of these attacks have taken place so far. Novorossiysk in the Black Sea has been a target as well as other locations in the Black Sea as well up north in the Baltic Sea. These attacks involve limpet mines, a World War I technology that persists to the present because they are simple, cheap and easy to deliver. An underwater diver swims, often astride and underwater swimmer delivery vehicles. Limpet mines are attached to a ship’s hull using magnets. The mine has a timer, which the diver turns on before swimming away. At least four tankers and one cargo ship have been attacked. The timers on these mines caused the ships to suffer damage while at sea. One such event took place off Libya, another off Turkey and a mined vessel sank in the Mediterranean. Russian port officials responded by instituting hull inspections of arriving ships. So far no one has been identified as the culprit and no one has claimed responsibility. Russia has a long list of enemies but the Black Sea involvement seems to indicate another action by Ukrainian special operations forces.

For over a century naval mines have been used to defend and attack. The last great anti-shipping campaign using naval mines occurred during World War II. The mines were used frequently between 1939 and 1945. After the war, the U.S. analyzed its operations against Japanese shipping and found that submarines were important but not the only weapon effective against shipping. Some 8.9 million tons of Japanese shipping was sunk or seriously damaged and disabled at the end of the war. Submarines accounted for 54.7 percent of this. But 16.3 percent was attributable to carrier-based aircraft, 14.5 percent to land- based planes, and 9.3 percent to mines, most of them dropped by B-29s. Less than one percent was due to surface gunfire and the balance of 4 percent was caused by accidents.

Because of their ability to operate in enemy-controlled, by land-based aircraft, waters, submarines accounted for about 60 percent of the damage until the final months of the war. Then, during late 1944, carrier task forces went deep into enemy controlled areas, defending themselves against land-based warplanes and sinking a large number of ships. After April 1945, Japanese shipping was restricted to the Korean and Manchurian runs and to shallow coastal waters. At this point the naval mines dropped by B-29s in Japanese harbors and inland waterways accounted for 50 percent of all ships sunk or damaged. That was then, but eighty years later the United States is able to monitor large ocean areas and has aircraft that can quickly attack anything that's spotted.

Some 25,000 naval mines were placed by aircraft or submarine around Japan in 1945. Only about half were cleared after the war. Much of this work was done by demobilized Japanese sailors operating their old mine clearing ships as civilian contractors. The clearing was greatly aided by the U.S. providing the general location of all the mines put in place by aircraft and subs. Half the mines dropped in rarely trafficked waters were left in place because by the end of 1945 their sensors no longer worked and they were no longer a danger unless violently disturbed. Since this was the pre-GPS era, a lot of the mine locations were approximate and over the following decades tides, currents, and storms moved a lot of these shallow coastal water mines and some ended up in more heavily used waters where they are being rediscovered. If one of these old mines is discovered in shallow, well trafficked waters, they have to be destroyed before a ship or a ship anchor disturbs it. Sport divers are another danger, even though local divers are usually warned about old mines.

There are many other old World War II explosives found off Pacific islands. For example, some 800 meters off the coast of Okinawa, a World War II phosphorus bomb finally went off without any human intervention. The bomb had been dropped into shallow coastal waters in 1945, when U.S. troops invaded the Japanese island. Decades of tidal action and storms moved the bomb to shallower waters, until, exposed to the air, the phosphorus ignited, surprising people on the nearby beach with a column of white smoke. Japanese bomb disposal teams showed up to deal with it and found another unexploded bomb nearby, as well as a 105mm artillery shell. There are still unexploded bombs, shells, and grenades found on Okinawa.

Meanwhile, there are plenty of other Pacific battlefields where bombs are also being found. On the island of Guam, a U.S. territory, construction workers discovered a World War II era thousand pound/455 kg bomb, when their backhoe hit it. The bomb didn't go off, and bomb disposal technicians determined that it was safe to leave it alone until the weekend, when they would try to remove the fuze and then move the bomb. If the bomb could not be moved, it would be detonated where it was found. A bomb that size has about 295 kg of explosives. Thus when the bomb technicians went to work on the bomb, all people living or working within a thousand meters had to move so they were at least 1,600 meters from the bomb. Or move away at least 1,000 meters and stay indoors while the defusing was underway.

The bomb disposal teams on Guam are still called out, eighty years after World War II ended. It's worse in Europe, where hundreds of World War II explosives are unearthed each year in Germany alone. Usually there are no casualties, as bomb disposal technicians are well trained and get lots of practice. But the fuzes that did not go off in the 1940s are now getting old and more prone to detonation while being disabled. Detonating bombs in place is often expensive because it means evacuating lots of people and exposing homes and businesses to bomb damage.

The limpet mines recently used against Russian ships do not linger. If any fall or are shaken off a ship hull, it is unlikely to do any damage in the future. The amount of explosives is small and the detonation mechanism quickly becomes corroded and useless when in salt water.