Artillery: 120mm GPS Shell Finally Arrives


July 26, 2012: After over a decade of screwing around and dithering the U.S. Army finally got guided (APMI) 120mm mortar shells into combat. A year ago some APMI shells were fired in Afghanistan and it was discovered that some more tweaking was needed. Last April a regular (set up on the ground) 120mm mortar in Afghanistan fired some APMI rounds successfully. Recently a Stryker Brigade recently began using the APMI guided rounds from 120mm mortars mounted in Stryker wheeled armored vehicles. So far this year the APMI rounds worked as advertised in combat.

Development and production delays kept this from happening for years. But some pressure from the top (in response to lots of pressure from the bottom) made it eventually happen. It turned out that the new shell performed better than its specifications (the shell falls within a 10 meter/31 foot radius at least half the time). That was good news because Afghanistan is a place where 120mm mortars are very useful and a GPS guided 120mm mortar shell was seen as very helpful for avoiding civilian casualties and reducing the amount of ammo you have to truck in.

The troops have become used to GPS guided ammunition and the 120mm mortar has just enough explosives to take out most targets, if the shell is GPS guided. Moreover, each American motorized or mechanized infantry battalion has 4-10 120mm mortars, giving battalion commanders his own GPS guided weapons. This is a big deal. Precision weapons like smart bombs and GPS guided rockets and shells gives the user an enormous combat advantage and saves the lives of many nearby civilians.

It was two years ago, after over a decade of searching (and procrastinating), that the U.S. Army finally selected a GPS guided 120mm mortar shell, from one of three suppliers (two American and one Israeli). All the systems were similar. The winner was one of the American systems, the RCGM (Roll-Controlled Guided Mortar). This one works by using a special fuze that includes a GPS unit and little wings that move to put the 120mm mortar shell closer to the target. Thus, all you need do to convert existing 120mm mortar shells to RCGM is to use the RCGM fuzes (which handle the usual fuze functions, as in setting off the explosives in the shell, in addition to the guidance functions) in place of the standard fuze (which just makes the shell explode when it hits something).  The RCGM equipped shells cost about $7,000 each. The army promptly relabeled RCGM as APMI (Accelerated Precision Mortar Initiative). There are some things army procurement bureaucrats can do quickly.

To use RCGM you place the fuse into a device that loads the target GPS coordinates, then screw the fuze into the shell, and fire the shell. It would also be possible to program each fuze once it is screwed into the shell, via a metal probe that would go into a hole in the fuze, transfer the data, and signal that the transfer was accurately made.

As a result of adopting the RCGM, guided 120mm shells just got a lot cheaper and easier to use. This is particularly crucial for 120mm mortars, which are used by units close to the front lines, where not a lot of ammo can be carried and resupply is riskier since the enemy is so close. Thus a guided 120mm shell means fewer shells getting fired to get the job done.

RCGM is not the first attempt to produce a guided 120mm mortar round. The army has been working on a guided 120mm mortar shell for a long time. Five years ago the U.S. sent XM395 laser guided 120mm mortar rounds to Iraq and Afghanistan for testing. The XM395 Precision Guided Mortar Munition had been in development for 13 years and was almost cancelled at least once because of the delays. The 17.3 kg (38 pound) XM395 round has a range of 7.5 kilometers and will land within a meter (three feet) of where the laser is pointed. The problem with laser guidance is that the enemy often hides somewhere the laser cannot reach (behind rocks or a building). GPS guided shells get around this problem.

Unguided mortar shells cannot put the first round as close as guided ones, and requires firing several rounds and adjusting aim before you get one on the target. Normally, an unguided 120mm shell will land anywhere within a 136 meter circle (on the first shot). The shells that did not come close enough often hurt nearby civilians or even friendly troops. The GPS guided shell gets it right the first time. A guided mortar round is very useful in urban warfare, where a miss will often kill civilians. The 120mm mortar round has about 2.2 kg (five pounds) of explosives, compared to 6.6 kg (15) pounds in a 155mm shell. The smaller explosive charge limits collateral damage to civilians. While the laser guided round will land within a one meter circle, the GPS guided one lands within a ten meter (31 foot) circle. The GPS round is deemed the most useful, especially since the troops are satisfied with that degree of accuracy in GPS guided 155mm artillery shells, 227mm rockets, and JDAM bombs.



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