Excalibur: extended-range precision for the army.

November 2006, a Port City in Southwest Asia: While a Stryker Brigade is engaged in peace enforcement operations, separatists control a key road at the edge of town that feeds into the main markets. In defiance of a UN resolution, the separatists are using their checkpoint to screen various ethnic minorities and prevent them from entering the city. The separatists have set up a roadblock and are guarding it with a squad of soldiers armed with a heavy machine gun.

The Stryker Brigade Commander wants to attack the target, but he must take into consideration the proximity of-non-combatants and religious structures. With his effects coordinator (ECOORD), he determines the M982 Excalibur is the best means to attack the target.

A tactical unmanned aerial vehicle (TUAV) accurately locates the manned roadblock. Then a platoon of M777E1 joint lightweight (JLW) 155-mm howitzers from the brigade's direct support FA battalion located 25 kilometers north of the city receives the fire mission. After all non-combatants clear the checkpoint, the platoon fires three rounds of Excalibur in accordance with established criteria in the fire control system.

The rounds have the impact fuzing option and detonate from one to 10 meters from the separatist squad, killing six, wounding three and destroying the position. Because the impacts were so accurate, the closest buildings suffered only minor damage (broken glass) and none sustained structural damage. By employing Excalibur, the Stryker Brigade achieved its tactical objective without undermining strategic goals--decreasing the potential for a "CNN effect."

In this futuristic scenario, the JLW 155 battalion (USMC fielding in FY05 and Army in FY06) fired only three Excalibur rounds to destroy a key target. Today it would take many more rounds to achieve the same effects and likely would result in non-combatant casualties and other collateral damage. Excalibur will be the Army's first precision, fire-and-forget indirect-fire family of munitions. Excalibur munitions will be cannon-delivered, extended-range, self-guided projectiles. They will be global positioning system (GPS)guided and inertial measurement unit (IMU)-aided 155-mm munitions fired from digitized cannons.

Excalibur will be highly accurate. Target and fuze data will be programmed into the projectiles via an inductive projectile programmer, giving it 10 meters circular error probable (CEP) accuracy at ranges of at least 35 kilometers.

The projectiles will accommodate follow-on advanced technology submunitions and (or) guidance and control packages. Munitions planned for development are unitary, smart and discriminating. The first in the family of Excalibur munitions being developed is the XM982 unitary round, the subject of this article. It is projected for fielding as early as FY06.

Excalibur Unitary Munition. The Army's most recent operations have reinforced the need for responsive precision attack of critical point targets, to include those in urban environments or restrictive terrain, under all weather conditions while minimizing-collateral damage. The versatile Excalibur will give the Army that capability; it will have a high-explosive fragmenting/penetrating warhead that has an integral fuze capable of airburst, point-detonating or point-detonating with delay-fuze options. (See Figure 1.)

Excalibur will be stored, requisitioned and distributed through the Class V ammunition supply system that supports the Objective Force. The projectile will require no scheduled maintenance and accommodate technical updates at the depot level to preclude obsolescence. This "technical refresh" will improve the projectile as better technology becomes available, such as an enhanced GPS or IMU capability.

The round will be fired at high-angle quadrant elevations (QEs). High-angle QEs gain maximum acquisition time for the GPS receivers and for guidance components to make corrections along the guided portion of the trajectory. In addition, high-angle QEs optimize range.

Throughout its flight, the round's GPS position coordinates will be fed into the IMU to steer the round to the target. In the event the GPS signal is jammed after it's acquired, the IMU will use the last data available to fly the round accurately to the target.

Upon leaving the tube, the basal fins will deploy to stabilize the projectile; soon after, the four-axis canards will deploy, moving independently. In conjunction with the slipping obturator, the canards will reduce the "roll-rate" or spin of the projectile. This will allow the round to orient its GPS antennas toward the satellite constellation for rapid acquisition of the GPS signals. The canards then will glide or "fly" the projectile to the target.

Excalibur's guidance system will account for winds while gliding. As it nears the target, the round will orient itself to an almost perpendicular angle of attack to the target (which optimizes the blast effects). The fuze will function according to the option selected, and the high-explosive round will detonate on the target. The round's objective accuracy is a plus or minus 10-meter CEP at any range in its operational sequence. Figure 2 depicts its operational sequence.

Precision will make the Excalibur unitary the indirect-fire projectile of choice for point targets requiring fragmentary effects and for penetrating urban structures. Its fragmenting warhead will be effective against personnel and light materiel targets, such as dismounted infantry and weapons crews, air defense systems, radars and wheeled vehicles. Its ability to penetrate targets will allow for the warhead's maximum effects inside structures, such as command posts.

Tactical Applications. As with many munitions, target description is a key factor in the decision to use Excalibur. But unlike other cannon munitions, target environment is also a key factor.

Excalibur will be the munition of choice when the following requirements or conditions exist--

* Collateral damage must be minimized. Commanders will be able to engage targets with the Excalibur unitary in urban operations, making the most of the round's accuracy to limit collateral damage to the immediate target area. For example, it will be the optimum munition when the enemy uses "hugging tactics" --operates on the periphery of schools, hospitals, churches or congregations of innocent civilians.

* Complex terrain limits conventional projectiles' effectiveness. Excalibur's accuracy and fuzing options will allow commanders to engage targets protected by these terrain variations.

* The target is beyond the range of conventional cannon projectiles. Often Excalibur will be the only cannon projectile able to range a given target.

* Precise fires on an objective must be maintained to allow friendly assaulting troops to close to within 150 meters of their indirect fires.

* Tactical or survivability considerations require platforms to fire from compartmentalized terrain (forest, defiles, urban areas, etc.), in a direction other than directly on line with the target. The self-guiding projectile will travel nearly vertically (high-angle) as it leaves the firing platform and then alter its flight path (left/right, up/down) to reach the target location.

Target Location Requirements. Of the five requirements for accurate, predicted fire, "accurate target location" will become the most critical for employing Excalibur. Because the round isso inherently accurate, the target must be located accurately. Firing Excalibur at an imprecisely located target will result in its precisely missing the target.

The precision of Excalibur dictates the optimum target location error (TLE) be plus or minus 20 meters to defeat targets with fragmentary effects (a 30-meter TLE is acceptable for engaging exposed personnel) and a plus or minus 10-meter TLE to strike targets within structures (requires a direct hit) and lightly armored targets.

The target acquisition systems on the Knight (formerly called "Striker"), Bradley fire support team vehicle (BFIST) and Comanche helicopter are able to provide this target location accuracy. The future combat system's (FCS') reconnaissance and surveillance platform and TUAV also will be able to achieve these TLE accuracies.

While a failure to receive the GPS signal is remote (which would produce a ballistic, unguided trajectory that won't detonate upon impact), fire supporters must plan for it. A 500-meter radius free fire area (FFA) can be established over a "fail-safe" location to allow the round to safely impact if the GPS signal fails to be acquired. (The fail-safe areas are illustrated in Figure 3 as FFAs 1, 2 and 3.)

The fire control system computes the fail-safe location based on the firing solution. The gun and tube orient toward the FFA without affecting the round's accuracy as the round guides itself to the target. As with other indirect fire munitions, all other fire support coordinating measures (FSCM) can be applied when using Excalibur.

Employment Options. Figure 3 depicts a task force zone in which Targets A and B have been located and selected for attack with Excalibur. Howitzer Platoons 1 and 2 have been chosen to fire these missions. Theater rules of engagement (ROE) strictly limit collateral damage and require positive identification of combatants for indirect fire targets before engagement.

Target A is a communications and command and control ([C.sup.2]) node in a densely populated urban area. ATUAV has located it precisely, and a patrol has confirmed the target with "eyes-on."

Target B is the command post (CP) of a lightly armored battalion-sized force near the edge of the city in an assembly area. The force is not dug in, but it does have local patrols and perimeter security. Friendly forces have positively identified the target. This target is in fairly well-concealed, but not covered, and is in close proximity to farmhouses and a school on the edge of the city.

1st Platoon engages Target A, the commo and [C.sup.2] node, and 2d Platoon engages Target B, the CP. With the rounds programmed to glide to their respective targets, they are aimed toward FFA 2. (FFAs 1 and 3 also were aiming options.) The guidance system will correct the course of the round to its target. Aiming toward FFA 2 is only a safety precaution.

From a single, high-angle gun-tube orientation, Excalibur projectiles can maneuver to attack targets anywhere in an inverted" heart-shaped footprint approximately 40 kilometers long and 60 kilometers across at its widest point with the bottom of the footprint to the rear of the platform. (See Figure 4.) The advantage is that cannon positioning and gun-tube orientation is not rigidly tied to the gun-target line or limited to clear fields of fire to engage targets accurately.

Cannons can fire from small clearings in the middle of a forest, from defilade positions or from behind a tall structure or cliff. These positioning options increase the flexibility and responsiveness of Excalibur fires and cannon survivability. The Excalibur unitary projectile will give Field Artillerymen new ways of delivering steel on target. However, the mission remains the same: provide responsive, effective fires in support of maneuver operations.

The versatile Excalibur unitary round will give the maneuver commander more options for effects across the spectrum of conflict when fighting an enemy in the contemporary operational environment (COE).

Major Danny J. Sprengle, Army National Guard (ARNG), a Title 10 Active-Guard-Reserve Officer, is the User Representative for the Excalibur Program in the Office of the Training and Doctrine Command (TRADOC) System Manager Cannon (TSM Cannon), Fort Sill, Oklahoma. He has served in various fire support positions and commanded C Battery, 6th Battalion, 1st Field Artillery, 1st Armored Division in Germany. He is a graduate of the Command and General Staff College, Fort Leavenworth, Kansas. He will graduate from the University of Oklahoma with a Master of Public Administration with a concentration in Emergency Management in April 2003.

Colonel Donald C. DuRant, US Army Reserve (USAR), is the Smart Munitions User Representative in the Office of the TSM Cannon, Fort Sill. He has 17 years' experience in Field Artillery Combat Developments. In the USAR, he is the Chief of Task Force Alpha, 2d Simulation Exercise Group, 1st Brigade, 75th Division (Training Support) at Fort Sill. He holds an MA in Management from Webster University, St. Louis, Missouri.