Mortars are an invaluable tool for infantry forces, but they aren't exactly accurate -- only half land within 136 metres of where they're aimed. That sort of success rate just won't do in Afghanistan, where minimising collateral damage is imperative. That's why General Dynamics built a mortar with pinpoint accuracy.
Mortars provide indirect (not line-of-sight) firing capabilities to infantry troops against both enemy positions and assets without having to rely on heavy artillery forces. Mortars are dumb-bombs that come in either finned or spin-stabilised varieties. Finned mortars utilise metal fletching to maintain its flight path, while the spin-stabilised version travels much as a bullet does when leaving a rifle barrel. Both types are fired at low speeds with high, arcing trajectories.
That's great when you want to fire upon an enemy base from behind the crest of a hill (as the Vietnamese did with great success in the siege of Khe Sahn), but makes actually hitting what you want on the first few tries more of a crap shoot than a turkey shoot. "Typically mortars are fired in volleys against an area target because of their inherent inaccuracy, but with APMI, you have the potential to destroy a target with only one or two rounds," Peter Burke, PEO Ammunition's deputy product manager, Guided Precision Munitions and Mortar Systems said.
Conventional 120mm mortar rounds have a Circular Error Probable (CEP) of 136 metres (that means that a 120mm round fired at maximum range will fall within a 136m radius of the target 50 per cent of the time). More advanced precision position and pointing systems reduce that radius to 76 metres, but that's still not accurate to use in tight quarters where collateral damage is possible. General Dynamic's newly developed APMI 120mm mortar round employs GPS targeting to achieve a CEP of less than 10 metres -- athough four metres is the average -- at a range from 1000 to 5000 metres. "APMI is a 120mm GPS-guided mortar cartridge that provides the infantry commander precision-strike capability, which he has never had before," said Burke.
The 120mm round, technically known as a Precision Guided Mortar Munitions (PGMM), is part of the US Army's Accelerated Precision Mortar Initiative (APMI), hence it's moniker the APMI XM395. It employs the standard M934 high-explosive payload and works with the normal M210 mortar system. However, this is the first mortar with an on-baord guidance system. The XM395 packs a GPS tranceiver in it's nose, and adjusts its flight path using computer controlled folding fins. What's more, the XM395's fuse can be programmed to explode at height, on contact or after a delay. Before the round is fired, its flight data is input using a handheld fire control computer.
A mortar team typically carries 25 HE rounds. But when supplemented with a couple of APMI rounds, soldiers will be able to do more with less. Instead of loosing multiple volleys against a single target, fire teams will be able to strike it with on the first try. "The 120 gives you a lot more room to work with," Burke said. "To fit all the electronics into smaller cartridges, with today's technology, is not feasible. They started with the biggest size to give us the most room to work with. Plus, you're getting the lethality of a 120, which is leaps and bounds above what a 60mm HE round can do." The APMI likely wont replace HE rounds altogether given that the newer shells cost $US10,000 a pop. While the US Army is already looking into adding this functionality to 155mm Excalibur artillery shells, themselves worth $US100,000 each, there are no current plans to add GPS navigation to the smaller 60mm and 81mm mortar systems. [Strategy Page - Defense Systems 1, 2 - Army - Defence Web 1, 2 - PRNewswire]