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Artillery: U.S. Army Picks A 120mm Winner
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April 28, 2010: After years of searching (and procrastinating), the U.S. Army has finally selected a GPS guided 120mm mortar shell. Recent tests of three such systems (two American and one Israeli) saw the U.S. ATK system win the contract. In development since 2006, ATK uses a guidance system that replaces the fuze (which is screwed into the front of the shell) with a larger unit containing the GPS and little wings that move to put the 120mm mortar shell closer to the target. Thus all you need to convert existing 120mm mortar shells to GPS guidance is the ATK fuzes (which handle the usual fuze functions, as in setting off the explosives in the shell, as well as the guidance functions.)

To use the ATK GPS system, you place each fuse into a device that transfers 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 that the transfer was accurately made. The GPS guided fuze will put the shell within six meters (and usually much less) of the coordinates entered.

Because of the GPS fuze, 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.

ItÂ’s about time, because the army has been working on a guided 120mm mortar shell for a long time. Three years ago, the U.S. sent laser guided 120mm mortar rounds to Iraq and Afghanistan for testing. The XM395 Precision Guided Mortar Munition had been in development for twelve years, and was almost cancelled at least once because of the delays. The 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. This high accuracy is achieved because the XM395 uses laser guidance in addition to GPS. But this was more complex, expensive and difficult to use than the army required. What was needed was a mortar round that just provided consistent GPS accuracy (landing within 10 meters of the aiming point).

Unguided mortar shells cannot put the first round that close, and requires firing several rounds, and adjusting aim, before you get one on the target. 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 charges limits collateral damage to civilians. The XM395 was tested in Iraq and Afghanistan last year, but since it required someone nearby to use a laser designator, it was considered to have limited usefulness. Thus the push to get a GPS guided shell into service. Normally, an unguided 120mm shell will land anywhere within a 136 meter circle (on the first shot). The laser guided round will land within a one meter circle, and the GPS guided one with a ten meter 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.

Most U.S. infantry battalions are equipped with 120mm mortars. The army would like to get the GPS shell system into service by the end of the year. But the other two GPS shell manufacturers can challenge the results of the competition, and demand another opportunity to win. This can go on for a while.

 

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Az75       9/21/2010 2:39:56 AM
Incorporating precision guidance electronics into a single-use device, when one could do so much more effectively by incorporating the GPS into the sight (so the Mortar Btty/Platoon knows the EXACT location of the tubes) is much less expensive and would be a hell of a lot more effective. Incorporating it into the sight, allows for the precision targeting of the tube without needing posts or the rest. It would also work on the 81/120mm tubes as well as the GPMG's. Makes a hell of a lot more sense than trying to hit targets with super expensive shrapnel made from electronic components.
 
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WarNerd       9/22/2010 4:22:06 AM

Incorporating precision guidance electronics into a single-use device, when one could do so much more effectively by incorporating the GPS into the sight (so the Mortar Btty/Platoon knows the EXACT location of the tubes) is much less expensive and would be a hell of a lot more effective. Incorporating it into the sight, allows for the precision targeting of the tube without needing posts or the rest. It would also work on the 81/120mm tubes as well as the GPMG's. Makes a hell of a lot more sense than trying to hit targets with super expensive shrapnel made from electronic components.

It is a lot harder than you think.  Sure you know the exact location of your tube and target, but you still need to get the tube at precisely the right angle and direction, and that still does not account for the variation in construction between shells and mortar tubes of the same type, propellant performance, etc. that cause 'scatter'.  A guided projectile can resolve all those because its corrections take place at the end of the trajectory, not before the projectile is fired.
 
And a GPMG is not an effective indirect fire weapon.
 
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doggtag       9/22/2010 7:18:38 AM

Where mortars are concerned, one must also take into effect the everyday weather: the farther the bombs are lobbed (high trajectory flight at relatively low velocity, when compared to other artillery types),

the more susceptible they are to being nudged away from the desired target area by even slight crosswinds.

All the fancy gadgets on the actual gun sights don't really amount to much if the weather, quite literally, throws you a curve ball.

 

As to the fuze approach itself: I actually personally favor the idea of systems like these: fairly simple systems that can be installed into a shell's nosewell just as any other fuze, turning anything from standard HE or even smoke and cannister/cluster types into  highly precise ( + or - 20m CEP is better than 50+m....) munitions,
certainly cheaper than purpose-built PGMs (precision guided munitions, like Excalibur for the 155mm guns).
 
In the US, the PGK Precision Guidance Kit program aims for a common family that fits both 155 and 105mm artillery shells.
At one point, one of the competitors in the PGK program spun off the tech to create 120mm mortar integration as well...
DARPA even has requested proposals for developing nosewell fuze-based adaptive control kits for shells down as far as 60mm mortars (query ODAM- Optically guided Direct Attack Munition), and there have been successful lab tests in 81mm mortar caliber as well...
 
Again, the benefit of these nose fuze systems being, you can pretty much mount them into any type of round: they aren't payload-specific like a purpose-built PGM.
 
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HeavyD       9/22/2010 7:21:50 PM
All the more reason the Stryker Mobile Gun System should have a 120mm mortar/gun.  Precision indirect fire as well as the precision of direct fire would be highly-useful.  Especially given that the anti-armor role of the MGS is vastly over-played.  Yes there is usually arty at the call, but the closer to the action the weapon system is the quicker the response, the lower the flight time of projectiles, the more effective the fire will be.
 
With MRSI capabilities, the target could receive direct and indirect fire at the same time.  Ouch.
 
Plus a Stryker with a 120mm mortar gun would hold more than 18 rounds...
 
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doggtag       9/23/2010 7:43:35 AM
Have argued countless times about that one: the rationale behind a fire support vehicle using a fairly low trajectory, high-velocity, tank-killing-capable gun,
when high-angle fire sometimes has superior advantages (lobbing shells over obstructions, etc).
My idea there is in taking this (NEMO)
and giving it a longer barrel like this (2S31 VENA) that would allow milking a higher velocity out of the rounds' propellant charges to satisfy those folks who feel gun-mortars would suck at some flat-trajectory target shots....
 
The PGM compatibility is obvious:
 if it's not a fully automated system (which NEMO mostly is) and allows ease of manual loading from inside (like the VENA),
then something like Israel's LAHAT,
or renewed interest in the US' MRM project
(although both obviously would need a modified propellant system more compatible with the lower-pressure tolerances of the gun mortar) 
should satisfy the MBT killer crowd (although it's always been argued to me that the Styker BCT's Javelin dismounts are the primary AT system, not the MGS' APFSDS-capable M68-derived105mm...).
 
If they could ever effectively create a smoothbore HESH/HEP type round,
such a 120mm could also satisfy the demolitionists and obstacle breaching freaks as well...
I also think it wouldn't be a bad idea to equip X number of Bradleys with such a system also
(turreted, direct-fire-capable gun mortar), replacing their dismount section with one or two loaders and a sizeable rack of ammunition.
(I've often found myself wondering if Bradleys could accomodate a BMP-3-like turret,
but housing a 120mm gun mortar and 25mm M242 (or 30mm M230?) Chain Gun instead, and getting rid of the big cumbersome-to-reload TOWs altogether...).
 
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HeavyD       9/23/2010 7:15:34 PM
Bingo, Dogtag.
 
Sometimes dropping an air-bursting 120mm over a wall is far superior to blowing holes through it.  Better yet, be able to do both simultaneously with a NEMO-equipped Mobile Gun System.
 
Hell, I've argued that we should replace half of the L44/L55 120's with NEMO type systems on our M1A2's, because first and foremost the role of a tank is to support infantry operations.  Especially when there are no enemy MBT's to shoot at.  We can kill enemy MBTs with Javelins, Stryx, Copperheads, TOWs, Hellfires, Apaches, A-10's, UAV's brilliant submunitions etc, as well as our remaining MBTs.  We don't need a Stryker's 105 which is suspect against front-line MBTs anyway, except at a distance that damn-well better be a first shot kill for the stryker crew's sake!
 
But in procurement, sexy usually wins.
 
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