A continuous-rod warhead is a specialized munition used as a part of anti-aircraft and anti-missile missiles.

Construction

Left: Rods arranged on mandrel prior to welding (single layer shown)

Center: Alternating welds completed and ready to receive explosives

Right: Representation of rod expansion due to detonation of explosives

In its most simple conception, consider a cylindrical form upon which an even number of individual steel rods are arranged. The rods are parallel to the axis of the form and completely cover it. Now at one end, weld every other rod to the adjacent rod. On the opposite end, likewise weld the rods in pairs but ensure when starting that the first pair of rods is not welded on the opposite end. When all rods are welded, the cylinder of rods may be covered with a light sheet metal jacket that will serve to hold all rods in place. Alternatively, the welded rods may be encapsulated with epoxy resin adhesive. The form may now be removed and in its place is cast a cylinder of high explosive.

Operation

When detonated, the high explosive imparts a momentum to the rods, thrusting them outward in an expanding circle. The rods are sufficiently ductile to allow the expansion without breaking the rods or the welded joints, the rods instead bending at these locations. At some intermediate point the ring will have a zig-zag (alternating direction) appearance within a cylindrical envelope. Upon ultimate expansion the ring is circular and contained within a plane. The ring will then break and ultimately tend to form one or more straight rods. Since the net momentum of the rod relative to the missile is roughly zero its effectiveness will rapidly diminish as the broken ring expands.

The effect of this rapidly expanding ring upon contact with an aircraft is much more devastating than the conventional shrapnel used in earlier weapons. It is almost assured that any portion of the aircraft intercepted by the expanding ring will be completely dissected, including wiring, fiber optics, cables, and hydraulic lines, no matter how redundant they are. This assurance applies only as long as the ring is unbroken, so multiple layers of rods are employed in practical weapons to increase the effective radius.

Deployment

The warhead is a major component of an anti-aircraft missile—10 to 15 percent of its overall length. It is preceded by a guidance system and is followed by a rocket motor. Directional vanes or wings are mounted on a control section positioned relative to the warhead as is appropriate to the weight distribution and aerodynamics of the particular missile. These vanes or wings are moved by the control system component under the direction of the guidance portion.

Employment

To be effective the detonation must occur sufficiently close to the target aircraft, so this type of warhead is used in precision radar guided missiles such as the AIM-120 AMRAAM, as such missiles will only have a "near miss" accuracy. Other missile types such as the heat-seeking Soviet designed R-60 or the US made AIM-9 Sidewinder will fly to and contact a heat source such as the tailpipe of a jet engine and so detonate sufficiently close to (or within) the aircraft as to allow the effective use of a simple high explosive or fragmentation type warhead, but the continuous rod warhead has also been employed on this type since it can transform a near miss (prompted by target maneuvers) into a kill.