Mortars have existed for hundreds of years, proving extremely useful in World War I where the high angle of flight of the shells made them an ideal weapon for the muddy trenches of the Western Front. The weapon's simplicity coupled with the ease with which it can be transported and operated means mortars are still in common use today but, although methods of calculating azimuth and elevation angles for targeting have improved, their greatest weakness still remains their lack of accuracy. Mortars are now moving into the 21st Century with U.S. Soldiers in Afghanistan set to receive a first-of-its-kind, GPS-guided 120mm mortar munition that can pinpoint targets at ranges of up to 6,300 m (20,669 ft).

The new mortar rounds, which the U.S. Army will deliver to soldiers in Afghanistan early this month, are the result of the Accelerated Precision Mortar Initiative (APMI) program that commenced after an urgent request from the field commander in Afghanistan in Feb. 2009 looking to pinpoint targets more accurately. GPS guidance was preferred over laser guidance as it would allow soldiers on the ground to more accurately target insurgents hidden behind ridges and rock outcroppings.

Current conventional mortar rounds used by the army only have an accuracy of about a 136 meter (446 ft) Circular Area Probable (CEP). This means that 50 percent of rounds will land within 136 m of the target, 43 percent will land between 136 m and 272 m, 7 percent between 272 m and 408 m and the proportion of rounds that land further than this is less than 0.2 percent.

The new 120 mm APMI precision rounds, which have been undergoing testing since late last year, have been able to demonstrate a CEP of less than 10 m at ranges in excess of 6,500 m to greatly improve accuracy and reduce the risk of collateral damage. This equates to 50 percent falling within 10 m of the target, 43 percent between 10 m and 20 m and 7 percent within 20 m to 30 m.

"This is designed for a precision capability such as against a sniper in a building, or enemies in a bunker or trench. If you were to engage with a conventional mortar round, you would have to fire 8-to-10 rounds to kill or suppress the target. With APMI, you will probably be able to do the same thing with one or two rounds," said Bruce Kay, Department of the Army Systems Coordinator, Mortar Systems.

ATK was awarded the contract to deliver the APMI rounds after a "shoot off" against two other competing companies early in 2010. Its Mortar Guidance Kit (MGK) design converts M934 mortar bodies into precision mortar rounds by replacing standard fuzes in the mortar's fuze well and adding GPS guidance and navigation capability

The APMI rounds won't completely replace the conventional rounds in the field, which will still be required for area and suppressive fires. The U.S. Army plans to deliver a total of 5,480 APMI rounds to Afghanistan and they could be expanded beyond Afghanistan once they have successfully been demonstrated in combat.