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Bottom Feeders
by James Dunnigan
December 30, 2011

In the last decade the United States Navy and many of its allies have devoted a lot of attention and cash to one of their greatest dangers, naval mines. The more dangerous bottom mines (which lie on the bottom of shallow coastal waters) require different tools to find and destroy them. However, many areas along the coast are too deep for the bottom mines (which are ineffective in waters more than 26 meters (80 feet) deep.

As a result there has been a major change in how to deal with this problem. Instead of the old system, where a small force of mine clearing ships and helicopters were kept in readiness at a few bases, new mine clearing equipment will be on warships at all times. Currently it can take days or weeks to get mine clearing equipment to ships overseas that need it. In addition, the United States is replacing its two dozen mine hunter ships with LCS (Littoral Combat Ships) carrying mine hunting and clearing equipment.

But the most radical innovations are the portable mine hunting gear that any warship can carry and use. The key technology here is the use of miniature, unmanned, submarines. These USVs (unmanned seagoing vehicles) come in many sizes and models. One of these new mine hunting systems, the RMS (Remote Minehunting System), was developed during the 1990s and has been entering service with U.S. ships over the last decade. RMS is a miniature robotic submarine (7.4 meters/23 feet long, 1.1 meter/four feet in diameter) that runs just below the surface, with only a mast (for getting air to the RMS's diesel engine and to hold radio antennas and a video cam that looks out for obstacles on the surface) above the waterline. The front of the RMS holds a sonar that helps with navigation by looking for underwater obstacles. RMS tows an AQS-20 variable depth (it can change its depth to get better coverage) sonar. This system maps an area, showing where objects that might be mines are. RMS carries enough fuel for 24 hours of operations at a speed of about 20 kilometers an hour. RMS can be set to survey an area and return to the ship that launched it. A controller on the ship can give RMS specific navigation commands or change earlier ones. In many cases the RMS survey will show areas free of any suspected mines and this allows friendly ships to go where they want to. The AQS-20 has been upgraded to include an underwater camera that will broadcast back to the ship high resolution images of underwater objects.

To destroy bottom mines (which sit on the seabed), another mini-sub system is used. SeaFox is a small (1.4x.4x.2 meters/55x16x8 inches), battery powered sub that has a fiber-optic cable connecting it to a hovering helicopter. There, the controller can move the SeaFox close to a suspected mine (using a small sonar unit to assist navigation), then turn on a spotlight for a video cam to examine the object and determine if it is a mine. If it is, SeaFox gets closer and detonates a shaped charge explosive, sending a shaft of hot plasma through the mine destroying it (and the SeaFox, which is meant to be expendable.)

For moored (floating just below the surface and kept in place by a cable attached to an anchor) mines, there is RAMICS (Rapid Airborne Mine Clearance System). The original idea was for a SH-60 helicopter, armed with a 20mm cannon, to fire a shell into a mine submerged up to 13 meters (40 feet) underwater. When the projectile penetrates the mine it releases chemicals that cause the mine to explode. The exact location of the mine is determined via ALMDS (Airborne Laser Mine-Detection System). This is a laser mounted on the same helicopter that can penetrate the water to about 13 meters and produces a video image that is sent back to a nearby ship for real-time analysis. If a mine is discovered RAMCIS is used to destroy it.

Early on there were doubts that the 20mm shells could penetrate that much water and still have enough energy left to penetrate the mine casing. One option was to use a 30mm cannon instead, but it was feared that the larger caliber cannon would cause more vibration than the helicopter could handle. The solution was found in having the 30mm cannon fire one shell at a time and use a special shell design that penetrated the water without losing as much energy. Software improvements made the 30mm MK44 Bushmaster II cannon much more accurate. In subsequent tests seven of eight shots hit the underwater mine.

The helicopter, equipped with the RAMICS/ALMDS gear, will operate from LCS ships or any other ship with a helicopter pad. The navy is also looking into using unmanned helicopters for the job as it mainly consists of flying a pattern until a mine is found. If no mines are found the area is declared free of surface mines.

SeaFox and ALMDS are in service and RAMICS is just now being installed. The helicopters carrying SeaFox and RAMICS/ALMDS can be operated off any ship that can handle choppers, although in the future the LCS will carry it and all the mine hunting equipment. There are several other new mine hunting systems under development, most of them involving USVs. These are seen as ideal for mine hunting. One is being developed that can be operated from a nuclear submarine. Naval mine technology isn't standing still, though, as new designs are proposed that come equipped with weapons to defend themselves against the new generation of mine hunting gear. But in the next decade the mine hunters will have an edge they have not had for decades.

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