M864 Base Burn DPICM

Compatible with all fielded US 155mm artillery systems, the M864 is a dual-purpose improved conventional munition designed for extended range engagements. The M864 is capable of delivering 72 dual-purpose (anti-armor/anti-personnel) grenades to the target area. The 155mm M864 is the U.S. Army's long-range cargo round. It is the successor to the M483 and features a base bleed system that extends range without the inherent inaccuracy limitations of rocket assist motors. The M864 delivers a payload of 72 M42/46 Grenades to 28.4 km, and provides over a 200% increase in area coverage over the M483A1.

The M864 is a separate loading munition with a streamlined forged steel ogive, a low-drag steel body of either 1340 or 4190 alloy profile and a steel base closure. A gliding metal drive band encircles the rear of the body.

The M864 projectile is a dual-purpose ICM projectile that incorporates base burn technology to increase its range. The projectile is capable of delivering 24 M46 and 48 M42 dual-purpose anti-materiel/anti-personnel grenades at ranges out to 29 kilometers.

It is a base-ejection projectile that carries 72 DP grenades (48 M42 grenades and 24 M46 grenades). The grenades provide the projectile's dual capability. However, a third effect can be achieved by replacing the original expelling charge with a spotting charge designed to detonate the entire projectile as if it were a bulk-loaded HE item. Once fired, the propellant ignites the base burner unit, which expels hot gas and increases the projectile's range. At the predetermined time in flight, the grenades are expelled, and they arm themselves while falling. They function upon impact.

The M864 has a forged-steel body with a base plug, an ogive, and a universal lifting plug. The color code for the M864 projectile is an olive-drab body with yellow diamonds and markings. Its DODIC is D864.

The M864 achieves extended range through a solid propellant, non-propulsive base drag reduction system. Talley's quick cure propellant processing, burn rate tailoring and improved inhibitor systems have been key to program success.

Base burn technology was developed to reduce the amount of base drag on a projectile, thereby increasing the achieved range. The drag is reduced by a (base) burner unit located on the base of the projectile. This extended range system consists of small amounts of combustible material in an enclosure that is attached to the base of the projectile. After firing, the combustible material is exhausted through holes in the base of the projectile thereby increasing pressure in the base region and increasing the range of the round. Once ignited, the base burner unit bleeds hot gas which causes the flow of air at the base to be less turbulent. The decrease in turbulence causes less base drag. (Base drag accounts for about 50 percent of total drag.) The amount of thrust produced by the base burner unit is negligible and does not serve the same function as the rocket motor on RAP.

The M864 Base Burner Assembly utilizes a Talley HTPB/AP propellant developed and tailored specifically for Base Burner artillery applications, and has been successfully gun tested at -60 degrees F to +145 degrees F. Talley created a specially developed HTPB compatible inhibitor system to provide superior bonding during temperature cycling and gun launch conditions.

The M864 projectile is not ballistically matched to any projectile currently in the inventory, but because of the similarity of the trajectories, firing data for the M864 can be determined from the M549A1 firing data.

Approximately, 30,000 of these rounds were shipped to the Gulf in Operations Desert Shield and Storm. But, at that time, BCS didn't include the M864 in its software and the round required units to use unfamiliar provisional tabular firing tables (TFTs) to compute its firing data. Consequently, units didn't fire the M864. In addition, because the M864 has the same training restrictions as the M483A1, by the late 1990s the M864 was still a mystery to many Redlegs.

The M864 complements the M483A1, increasing range to 28.2 kilometers and area coverage by 200 percent. Additionally, the base burner unit achieves its extended range through a solid propellant non-propulsive base drag-reduction system-not through added propulsion as in RAP. The reduced drag is the result of gases being expelled from the base burner unit.