Defense Media Network

Precision Guided Munitions (PGMs)

The bulk of public attention to the increasingly important area of precision guided munitions (PGMs) has been focused on the U.S. Air Force and Navy. Videos of ship- or aircraft-fired missiles striking their intended targets dead-on – in some cases, even to the extent of flying into a specific window in a multi-story building – have become commonplace.

It is a reversal of status for the Army and Marine Corps, once seen as the most precise instruments of war because of their proximity to the enemy on the ground. As missiles and rockets became more precise, however, tanks, cannon, mortars, hand grenades, etc., replaced “dumb” bombs and ship guns as area suppression weapons.

The less accurate the weapon, the higher the probability of “collateral damage” – killing or injuring non-combatants and damaging or destroying protected structures, such as hospitals, schools or religious sites.

While much of the fighting in Afghanistan has been in remote mountains, there have still been incidents involving villages and non-combatants, sometimes because weapons fire overshot the enemy target and struck someone or something in the valley below. In Iraq, meanwhile, most combat in recent years has been urban, with the enemy using civilians and off-limits targets as shields.

As the rules of engagement (ROE) for U.S., NATO and allied forces in Afghanistan became decidedly more restrictive in 2009, insurgent forces became increasingly blatant about firing from within such protection.

During World War II, collateral damage was part of the attack strategy, from the carpet bombing of German cities to the atomic bombs dropped on Hiroshima and Nagasaki. It was a psychological weapon, putting pressure on the enemy leadership to stay away from such areas or to surrender to avoid future attacks.

Such tactics not only have little impact on the kind of enemy now being fought in Southwest Asia, but the backlash from collateral damage, especially in Afghanistan, can turn civilians who were not assisting the insurgents into lifelong enemies.

As a result, the Army has been developing its own PGMs and precision strike capabilities, working with the Defense Advanced Research Projects Agency (DARPA), as well as the Army Armament Research and Development Center (ARDEC) and Program Executive Office-Ammunition (PEO-Ammo).

Precision strike might be defined as the ability to select from various PGMs to hit a specific, often small, target with little or no collateral damage. In concept – and, increasingly, in practice – that has meant dramatic improvements in the accuracy of everything from the individual soldier’s weapon to tanks and field artillery.

One of the first of the latter to be fielded was the Excalibur 155mm Precision Guided Extended Range Artillery Projectile, which began development before 9/11 but did not deploy to Iraq until 2007 or Afghanistan until 2008.

“Instead of focusing on CEP (circular error probable) that allows for target misses up to 60 meters (196 feet), we’re redefining what precision means to the warfighter today,” says Steve Bennet, program director for Excalibur prime contractor Raytheon. “Precision means consistently impacting the target within 10 meters (32 feet). Excalibur provides the warfighter with precision that is essential to the protection of civilians and combat forces.”

Even that definition is sometimes insufficient for the demands of the current battlespace, however.

In its most recent series of tests on the Excalibur Ia-1 projectile, fired from a Paladin gun system at the Army’s Yuma Proving Ground in Arizona and using an enhanced Atlantic Inertial Systems inertial measurement unit (AIS IMU), the Army reports consistently hitting within 2 meters (6.5 feet) of targets at ranges from 8-12 kilometers (4.9 -7.5 miles).

The Ia-1 currently is deployed to SW Asia and the longer range Excalibur Ia-2, with similar accuracy, is scheduled for fielding in the Fall of 2010.

According to the Army program office, troops in Afghanistan are especially happy with the ability of the Excalibur to bring quick and accurate effects against an enemy target without needing to call in the Air Force.

A major advance for Army systems has been the development of guidance systems small enough for use in tank guns or field artillery, but also able to handle the extreme “gun shock” of being fired from such weapons.

Another concern has been over-reliance on GPS, which could be jammed, leaving the combatant commander with the same CEP-based area suppression fire capability of the past. That is the value of systems such as the AIS IMU and DARPA development efforts such as Micro Inertial Navigation Technology (MINT), Precision Inertial Navigation Systems (PINS) – with a primary application for individual foot soldier guidance without GPS – the Navigation-Grade Integrated Micro Gyroscope (NGIMG) and even the Chip-Scale Atomic Clock (CSAC).

Better, smaller, greater shock-resistance – in both GPS and alternate guidance systems – are combining to give the Army and Marine Corps the same level of precision strike from the ground the Air Force and Navy have long had from the air. That applies not only to big guns and smaller field artillery, but ultimately to the individual soldier, from PINS-derived guidance chips in combat boot insoles to “smart bullets”, such as DARPA’s EXtreme ACcuracy Tasked Ordnance (EXACTO).

“Great progress has been made on two key technical challenges – the ability to communicate with the bullet in flight and the ability to then change the bullet’s course,” says DARPA program manager Lyn Beamer.

“EXACTO will change the attack geometry profile in that it will allow persecution of targets that cannot currently be engaged because of range, terrain, wind, target motion or other factors. This will greatly increase the effectiveness of snipers, as their shot accuracy becomes independent of environmental conditions, while also increasing sniper safety by allowing much greater standoff distances.”


J.R. Wilson has been a full-time freelance writer, focusing primarily on aerospace, defense and high...