Continuous - rod warhead A continuous - rod warhead is a specialized munition that exhibits an annular blast fragmentation pattern , so that when it explodes it spreads into a large circle that cuts the target . It is used in anti - aircraft and anti - missile missiles . Early anti - aircraft munitions . Rifle and machine - gun bullet s were used against early military aircraft during World War I . Artillery was used when aircraft flew above the range of rifle and machine - gun cartridges . Since the probability of actually striking the aircraft was small , artillery shells were designed to explode at the approximate altitude of the aircraft to throw a shower of fragments in the vicinity of the explosion . Similar anti - aircraft weaponry with larger calibers , higher rates of fire , and improved fuze s continued to be used through World War II . These bullets and small fragments often made small holes in the airframe . Unless the bullet struck the pilot , the engine fuel or cooling system , or a wire or hydraulic line actuating control surfaces , the aircraft remained operational . Some anti - aircraft artillery projectiles were designed to fragment into long , thin pieces in an attempt to inflict damage on the airframe . Holes made by such fragments were more likely to cause destructive disruption of airflow around high - speed aircraft , but the hit probability was lowered for the smaller number of fragments from a warhead of equal size . The problem became more significant as anti - aircraft missiles were developed to replace guns after WWII . A smaller number of missiles would require an improved warhead to match the aircraft destruction probability of the larger number of artillery projectiles potentially carried by a weapon platform of the same size and cost . Some to increase probability of aircraft destruction . The concept of a folded continuous rod warhead was suggested in 1952 . Construction . An even number of individual steel rods are arranged in parallel to form a cylinder . The ends of the rods are welded together — the first rod and the second rod are welded together at the top , the second and third at the bottom , and so on all the way around the form . Operation . When detonated , the high explosive imparts momentum to the rods , thrusting them outward in an expanding circle . The rods are sufficiently soft ( ductile ) to allow the expansion without breaking the rods or the welded joints , and the detonation velocity is limited to under 1 , 150 m / s , allowing the rods to bend at these locations instead . 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 . This rapidly expanding ring , when hitting the aircraft , can be more effective than an equivalent fragmentation warhead : the ring ' s effectiveness decreases as 1 / R , rather than 1 / R ^ 2 for fragments . Portions of the aircraft intercepted by the expanding ring will receive a continuous cut through the skin , light structure , underlying cables , hydraulic lines , and other plumbing if present . This may cause a structural failure , or , if not , can be sufficient for defeating the redundancy of aircraft systems . The effect is only pronounced as long as the ring is unbroken , so multiple layers of rods are employed in practical weapons to increase the effective radius .