Pakistan is buying two used Tripartite-class minehunter ships from the Netherlands. Pakistan bought three of these vessels from France in the early 1990s, before production stopped in 1995. One of those three minehunters was completed in Pakistan with French assistance. Pakistan was the last country to receive newly built minehunter ships and was so satisfied with them that all three it originally purchased are still in service. Currently 23 Tripartite ships are still in service worldwide and six are in reserve, wanting for potential foreign buyers.
The Tripartite-class was so named because it was a late 1970s joint effort by Belgium, France and the Netherlands to develop a common design to be built in each country with some local variations. Each of the partners concentrated on one aspect of the ship. For example, France supplied most of the sensors and electronics while Belgium and Holland designed the boat structure, engines and mechanical equipment, Initially, sixty ships were to be built but production did not really get going until the first ship entered service in 1983. It had taken five years to work all the kinks out. By the late 1980s the naval mine threat from the Soviet Union was diminishing that that threat disappeared in 1991 along with the Soviet Union. Only 40 Tripartite ships were built, some for export. Many of these ships retired by the original three nations were refurbished and exported to countries that saw these ships as effective against local threats.
The 595 ton Tripartite-class ships were 51.8 meters (170 feet) long with fiberglass hulls and a top speed of 28 kilometers an hour. The crew of 55 was required for round-the-clock operations when seeking and destroying mines. These minehunters had a max range of 5,400 kilometers so they could move to distant trouble spots under their own power. The minehunters were very maneuverable and carried two PAP 104 remotely controlled UUVs (unmanned underwater vehicles) that searched for bottom mines. The UUV carried a 130 kg explosive device that would be placed next to a bottom mine and detonated when the UUV had moved away to safe distance. Over 500 of these one-ton UUVs were built and upgraded since the 1980s and many are still in use.
In the last decade all three nations that built Tripartite-class minehunters have come up with replacement designs. These are about the same size as the Tripartite ships but are called MCMVs (Mine Countermeasures Vessels) and have steel hulls. The MCMV uses unmanned surface and underwater vehicles to search for and destroy mines. This keeps the MCMV out of harmís way as it has become a mothership of USVs, UUVs and even some UAVs (unmanned aerial vehicles). More small warships (frigates and some destroyers) are carrying some of these UUVs for dealing with mines until the MCMVs can arrive.
The danger comes from cheaper and more capable bottom mines. A bottom mine detonates if a ship type it was programmed to attack is detected. The Mk-62 is the primary American bottom mine and a good example of what the threat is. The Mk-62 is basically a 227 kg (500-pound) bomb with a 32 kg (70 pound) battery, electronics and sensor package screwed on.
Once the Mk-62 hits the water, slowed down by a parachute if delivered by air, it sinks to the bottom. These mines are meant to be dropped in shallow coastal waters, harbors or rivers. Once on the bottom the Mk-62 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. With new battery tech this active life is apparently even longer. If you drop several Mk-62s in an area, some can remain 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 and Air Force warplanes regularly train dropping Mk-62s. Similar mines can also be delivered by submarines or surface ships. 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.
You need a high-resolution sonar that seeks out mines on the sea bottom, waiting for ships to pass over. The U.S. Navy has been using sleds dragged over the surface approach since the 1980s. The original sled system went through several major upgrades and is considered very reliable and effective. The MH-53E sled is still able to carry more equipment and sweep a larger area faster.
The U.S. Navy has also developed a complementary system, ALMDS (Airborne Laser Mine Detection System). Designed to operate from the MH-60S helicopter, ALMDS uses a Laser Imaging Detection and Ranging blue-green laser to detect, and identify naval mines near the surface. Unlike the AQS-24A, ALMDS operates from the low flying, and smaller, helicopters. Surface mines are either moored (via a chain to the bottom) or floating (a favorite terrorist tactic), and many float just below the surface. The laser works very quickly, and enables the ALMDS equipped helicopter to quickly check out large areas for surface mines. Terrorists have used naval mines before, of the floating variety. Navies tend to use the more sophisticated, expensive and hard-to-get bottom mines (that lie on the bottom, in shallow water).
The U.S. Navy has come to agree that minehunter ships are also very useful and are investing in unmanned surface and subsurface vehicles that can turn any ship into a minehunter.