MOUT weapons: the search for a new fire support weapon

Infantry Magazine, Fall, 2003 by Gordon L. Rottman

With the emphasis today on military operations in urban terrain (MOUT), it is surprising that there are no fire support weapon systems now in the inventory or under development that are truly optimized for that environment. There are a number of compact, single-shot, shoulder-fired rocket launchers are available that can blast holes through heavy building construction materials. These are ideal weapons for Soldiers who must have a way to defeat hardened enemy fighting positions and blow breach holes in buildings to permit entry.

Current Weapons

Today's infantry has a variety of excellent weapons that are useful in MOUT. The 40mm Mk 19 Mod 3 grenade machine gun has more than sufficient range in built-up areas, a high rate of fire, and excellence in providing suppressive fire. But even with high explosive dual-purpose (HEDP) projectiles, it lacks sufficient penetration of concrete and masonry. It will penetrate 12 inches of pine logs, 16 inches of sand-filled cinder blocks (two layers), and 20 inches of sandbags (two layers). Their behind-the-target effects, however, are somewhat limited.

Other weapons capable of breaching and defeating enemy positions within defended buildings include the M136 (AT4) light antiarmor weapon (LAW) and the XMI41 bunker defeat munition (BDM). The M136 has a high-explosive antitank (HEAT) warhead that makes it less than effective against fortified buildings. The BDM has an HEDP warhead, but it is a one-shot, disposable weapon like the M136. The BDM will penetrate 8 inches of reinforced concrete, 12 inches of brick (three layers), or 3 feet of tamped earth or sandbags (three layers) backed by 6-by-6-inch timbers. Besides destroying enemy positions, it can be used to breach walls for egress. The BDM has an effective range of 15-250 meters. The M98A1 Javelin surface attack guided missile system will defeat virtually any tank in the world, but it is extremely expensive to use for knocking out field fortifications.

There appears to be a sentiment among many that using high-velocity, rocket-propelled, guided or unguided weapons against MOUT targets is less than desirable. Whether the rocket's warhead is intended for antiarmor or anti-material (buildings, fortifications), such weapons are expensive, do not always provide the optimum terminal effect on the target, sometimes prevent firing from confined areas, and create a substantial backblast signature. The backblast also poses a hazard to the crew when fired at a high angle such as the upper floors of buildings.

A frequently suggested option it to resurrect the 106mm M40A1 recoilless rifle, which was the mainstay battalion-level antiarmor weapon until the introduction of the TOW system in the early 1970s. The Israelis and others still employ the 106mm and have used it effectively in MOUT. Provided with HEAT, high explosive plastic-tracer (HEP-T), and antipersonnel-tracer (AP-T) (flechette) rounds, it has been used effectively in MOUT operations by U.S. forces in Vietnam, the Dominican Republic, and other areas, but it also has limitations. It produces a major backblast signature and hazard, and this, coupled with its long barrel, restricts its use in built-up areas. Too, its design limits the way it can be mounted on a vehicle. It would be almost impossible to mount it on a HMMWV to allow 360-degree traverse, much less provide enough elevation to engage elevated targets. It would make little sense to field a weapon with inherently limited traverse. Its ammunition is heavy and difficult to manhandle.

What might be the most desirable characteristics for a highly mobile, vehicle-mounted, crew-served weapon capable of providing effective fire support in a MOUT environment? Preferably, this weapon would be effective for fire support in other environments such as deserts, plains, forests, jungles, hills, and mountains. Certainly no weapon can be ideal for all terrain and conditions, but one weapon can be effective for most.

Terminal effects

The terminal effects are, of course, the most important consideration. The most common construction materials in urban environments are hollow cinder block, brick (backed or not backed by wood frame construction), comparatively thin and lightly reinforced concrete, stone, timber, and wood frame. Stone, concrete, and masonry walls separating property (such as courtyards and compounds), rubble barricades, multiple-layered sandbags, and wrecked civilian vehicles may be used as protective cover by the enemy. High-velocity HEAT rockets are not necessarily the most effective warhead to use against such targets. HEAT round behind-the-target (barrier) effects are less than desirable with only limited fragmentation, both from the warhead and secondary fragmentation for the barrier materials. The penetrating plasma jet is narrow and will injure only those in its immediate path while generating only limited blast overpressure. Most HEAT warheads are relatively thin-walled, being essentially carriers for shaped charges. What we need is a more robustly constructed high explosive (HE) warhead on which a delay fuse may be fitted to allow it to punch through moderate building materials by kinetic energy and detonate behind the target barrier to inflict the maximum amount of damage by blast, fragmentation, and over-pressure. The availability of different types of projectiles is desirable as it provides additional target attack options and capabilities. Most rocket weapons and recoilless rifles are limited to HEAT or HEDP warheads.