WASHINGTON — The US Army has awarded Orbital ATK with a $120 million contract modification to make kits that turn conventional 155mm artillery into a near-precision shell.

The kits are meant to limit civilian casualties and collateral damage, allowing the use of artillery where it would have otherwise been ill-advised — in a congested area or near friendly forces.The guidance fuzes would be fielded to the Army, the Marine Corps, Australia and Canada. Deliveries are scheduled to begin in early 2016, following low-rate initial production, which began in January.

In 2006, ATK — which has since merged with Orbital — was awarded one of two technology demonstration contracts from the US Army to develop the XM1156 precision guidance kit (PGK) for the 155mm howitzer artillery system. In 2013, it won a $58 million contract, with a base requirement and two options for a year of full-rate production; the recent award was option one.

"The goal was to try to design a fuze that would also provide guidance that would just drop into the existing inventory because the Army has millions of rounds," said Tim Jones, PGK program manager for Orbital ATK. "To build new rounds — and there are programs like that — are very expensive, more than 10 times what PGK would cost."

The PGK fuze screws into the fuze well of 155mm high-explosive artillery projectiles. It uses a GPS to determine its position relative to the target and uses small aerodynamic fins to perform in-flight course corrections along its ballistic trajectory.

"Missions were being denied because of collateral damage concerns," Jones said. "The enemy isn't always out in the open, so artillery really had to improve accuracy to stay in the fight to the level the Army wants it to be."

Moreover, the unit price is less than $10,000, according to the company, which compares favorably to self-contained precision rounds that cost $70,000 to $130,000.

The accuracy of area fire weapons is based on circular error probability (CEP), the imaginary circle around a target within which a round would fall. PGK, according to the company, reduces artillery dispersion of more than 200 meters to less than 30 meters.

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"One of the reasons the program [receives] criticism is that it was in development a long time, but the Army saw the ability to go past 50 meters, the original threshold goal," Jones said. "In the end, we achieved, or exceeded the Army's goals."

Once of the engineering challenges, Jones said, was to miniaturize the fuze and GPS guidance system to fit inside the fuze well, with no other modifications to the 155 rounds. Ultimately, it weighs about three pounds, while the "dumb" fuze weighs two pounds — the difference being the fins and alternator.

The kit includes a "fail-safe" option to keep a round from detonating if it does not get close enough to the target.

The system is self-contained. There is no battery, but there is an alternator inside that lets the system generate its own power in flight, Jones said.

PGK passed first article acceptance testing in December , several months after the Army fielded it to artillerymen from Batteries A and B, 2nd Battalion, 15th Field Artillery Regiment, then deployed to Afghanistan.

According to Jones, the program has performed compatibility testing for international platforms and with countries that use US rounds.

"There's a tremendous amount of overseas interest and the US Army is interested in working with allies," Jones said.

During a September demonstration, PGK proved its compatibility and performance with the German Army's DM111, 155mm round fired from their self-propelled howitzer, PzH2000.