This month, several U.S. B-52 bombers practiced dropping naval mines off the coast of Guam, in the central Pacific. The bombers dropped 162 inert mines. The Mk-62 is a U.S. Navy weapon, and is basically a 500 pound bomb with a 70 pound electronics and sensor package screwed on.

Once the Mk-62 hits the water (slowed down by a parachute), it sinks to the bottom (the mines are dropped in shallow coastal waters, harbors or rivers) and its sensor package turns on. The Mk-62 is programmed beforehand to go after certain types of targets. Magnetic, pressure and sound sensors can identify a wide variety of ships, and only certain types are attacked. The battery on the Mk-62 powers the electronics package for a long time (the exact duration is, obviously, secret) but is reported to be at least weeks. If you drop several Mk-62s in an area, some can shut down until others run down their batteries. The software in the Mk-62 is extremely flexible and capable, and the sensors are all passive (they do not emit) making the mines hard to detect and clear.

Navy warplanes regularly train dropping Mk-62s. Similar mines can also be delivered by submarines. These mines can be decisive weapons, if used by a power that can deliver them quickly by air. For that reason, air force aircraft are equipped to carry the Mk-62s, and train dropping them.