For a decade, the U.S. Navy has been working on RAMICS (Rapid Airborne Mine Clearance System), for destroying moored or floating mines that are close to the surface. Until recently, they could not get the system to work as well as it should have (on paper). That changed when some software tweaks, a larger caliber gun, and a special shell design, were added to the mix.
The original idea was for SH-60 helicopter, armed with a 20mm cannon, would fire a shell into a mine submerged up to 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 40 feet, 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 us use a 30mm cannon instead, but if was feared that the larger caliber cannon would cause more vibration than the helicopter could handle. The solution was found in having the cannon fire one shell at a time, and use a special shell design that penetrated the water without losing so much energy. Software improvements made the 30mm MK44 Bushmaster II cannon much more accurate. In recent tests, seven of eight shots hit the underwater mine.
The helicopter, equipped with the RAMICS/ALMDS gear will equip 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.
The more dangerous bottom mines (which lie on the bottom of shallow coastal waters) require other tools to find and destroy them. Many areas along the coast are too deep for the bottom mines (which are ineffective in waters more than 80 feet deep).