Infantry Weapons Get Accuracy On-the-Move.

The most fundamental job of a soldier is to be able to shoot, move and communicate. To shoot on the move is even better.

Although advanced combat vehicles have improved technology that enables shooting on the move, much of that technology has yet to migrate to smaller, lightweight vehicles. Expensive stabilized gun sights in larger vehicles help crews hit the targets at which they aim. Although recent missions have increased the possibility of engagements with small-caliber weapons, from 5.56 mm to 40 mm, soldiers still aim and shoot those weapons the old fashioned way.

Shooting from a moving vehicle looks easy, or so it seems in films and television productions. But hitting a target while shooting from a moving vehicle is difficult in real life.

Stress and other human factors associated with shooting influence accuracy in the still prone position at a firing range. These impediments can be corrected through training. But shooting on the move adds other physical inhibitors that cannot be overcome by training. The muzzle of a small-caliber weapon moves when the vehicle moves. Vibrations from the wheels traveling over the terrain make the weapon move. Without some kind of stabilizing force to keep the weapon on target as the shooter pulls the trigger, the bumps, jerks and swerves of a vehicle on the move prevent the shooter from hitting the target.

As the bullet leaves the muzzle, it may or may not travel on the intended trajectory to the target. Recently, engineers at the U.S. Army Research Laboratory (ARL) have discovered a way to fix that.

By adapting technology normally found in the turrets of Bradley fighting vehicles and Abrams tanks, ARL engineers improved the accuracy of small-caliber weapons mounted on small, lightweight vehicles to an almostprone position level. They call their invention the inertial reticle technology (IRT), a replacement sight adapted to the 5.56 x 45 mm M16A2 assault rifle and the .50 caliber M2 heavy barrel machine gun. They mounted the modified Ml6A2 on a fast-attack vehicle most often used by Special Forces units, and mounted the M2 on a high-mobility multipurpose wheeled vehicle (Humvee).

Instead of the traditional scopes, weapon sights and mounts, the IRT uses a video camera with a display unit mounted inside the vehicle and a lightweight "weapon positioner". The positioner "drives" the weapon to change elevation and azimuth. Sensors attached to the elevation and azimuth axes of the weapon measure the position of the weapon in relation to the vehicle. Other sensors detect pitch, yaw and roll directions. Engineers attached a revolution counter on the Humvee and a wheel counter on the fast-attack vehicle to calculate the vehicle's relative relationship to the target. The shooter sees all this data on the video display.

The shooter inputs the initial range to target into the computer using a laser range-finder mounted on the weapon. Data displayed on a remote-control panel sitting on the shooter's lap indicates the aim point and a sight picture with the reticle. Sensors in the weapon positioner ballistically correct for range, elevation and azimuth. The rericle remains fixed on the target driven by the weapon positioner's sensors and the wheel or revolution counter. The shooter uses a simple joystick mounted on the remote control panel to put the reticle on the target and keep it there.

After setting the range and acquiring the target, the computer continuously measures the position of the reticle in relation to the aim point adjusting changes affected by movements from the vehicle. When the aim point and the rericle are aligned, the computer calculates the firing time. All the shooter has to do is set the range, aim and pull the trigger, activating an electronic solenoid that actually fires the weapon.

The ARL engineers adapted existing technology to create this system. They used a Sony video camera, a range-finder from Hellos, angle encoders from Itek and sensors from Systron Donner. They made their own wheel counters.

In test firings, at Aberdeen Proving Ground, using the M16A2 mounted on the fast attack vehicle, the project engineers found that firing from a stationary position matched the accuracy of firing from a prone position at the rifle range. However, in an initial test firing, on the move, at a speed of 16 kilometers per hour, at a stationary target, at a range of 400 meters, results were nearly three times less accurate than the stationary firing. Engineers discovered that a slight vibration in the weapon platform created an image of multiple rericles on the control panel. Adding a few bearings and springs helped stabilize the platform.

The test engineers tried firing at the target, on the move, from different angles, from the front and sides and while the target was moving. In every case, the system kept the weapon on target with 10-round groups between 43 and 48 centimeters, depending on the scenario. When they fired the same weapon from a standing position, their groups were between .28 and .30 millimeters.

The IRT could have significant implications for the application of small arms in military missions. Soldiers will be able to stay inside, in the comparative comfort and safety of their vehicles, while they select their targets, aim, shoot and strike. They will be able to engage targets on the move, faster and with greater accuracy than if they fired from the moving vehicle without the aid of a gun stabilized sight. That means they will not have to dismount to aim and shoot.

Virginia Hart Ezell is president of the institute for Research on Small Arms in International Security and a reserve Army major in the Ordnance Corps.