From Bazookas To RPGs
Since World War II, shaped charges have transformed warfare— and scientists still struggle to understand the nature of their deadly effectiveness
After subduing Czechoslovakia and dividing Poland with the Soviet Union in 1940, Adolf Hitler began laying plans for conquering the rest of western Europe. He determined that the most effective route around the Maginot Line and into Holland, Belgium, and France would be to open a gap through the Belgian line of fortifications between Liege and Maastricht. Hitler ordered 11 of a 42-glider attack force to touch down on a half-mile-long stretch of grass near the edge of a limestone cliff overlooking the Albert Canal. That field served as the roof of the mighty fortress of Eben Emael, cut into the cliff. Five-inch guns inside massive casemates lorded over three key bridges that crossed the canal.
The German glider unit would have only 10 minutes to take Eben Emael. Should the Belgian forces destroy the bridges before the attackers secured them, the blitzkrieg would remain the “sitzkrieg.” The fortress's thousand Belgian soldiers, protected by reinforced five-foot-thick concrete walls, 16-inch steel armor, and machine-gun posts and antiaircraft guns on the roof, seemed invulnerable even to the heaviest artillery and largest bombers. Below its mighty guns a smaller fort and garrison protected each bridge.
Shaped charges have begotten the world’s most destructive handheld weapons but have also wrought major civil innovations.
While the three other assault groups guided their gliders toward the bridgeheads, 78 men of “Group Granite” touched down on the roof, heaved the fuselage doors onto the grass, and darted into the darkness with guns, flame throwers, and metal containers containing "shaped charges," a new kind of explosive device never before used in battle. Even the few scientists who had worked with shaped charges did not understand how they worked. The Nazi soldiers spotted the 100-pound devices against the walls of five artillery casemates and 20 pillboxes, following a carefully numbered battle schematic.
Within 10 minutes, the charges had either destroyed the casemates and pillboxes or wrought enough damage for the Germans to press their advantage. Only one Wehrmacht officer, Lt. Rudolf Witzig, had known the secret of the new weapons, and a glider mishap had held him up, so the invaders were as astounded as the defenders at the effectiveness of the shaped charges. The Germans continued to assault the Belgians trapped in the lower reaches into the next day, but the German offensive had disabled the fortress's artillery and overcome bridge defenses in a matter of minutes. A critical gateway into the Low Countries now lay wide open.
Almost 70 years later, the tiny destroyer called the shaped charge is more potent than ever and still cutting through thick layers of armor and concrete in battle. In the meantime the technology has also found peacetime uses in building demolition, drilling for oil and gas, and space exploration.
The secret to its success remains entirely counterintuitive: taking away some of a charge's explosive material supremely increases its destructive power. Imagine a cylinder of solid explosive. Hollow out a conical cavity from one flat end, and then fit a thin metal cone into that cavity. The mouth of the cylinder is thus transformed into the muzzle of a hypervelocity gun when detonated from behind. Similarly sized Russian-made warheads, fired from the infamous RPG-7 shoulder launcher, can drill through a foot or more of steel armor. In a 1997 demonstration at the Nevada Test Site, a bigger shaped charge let daylight through 11 feet of steel armor. In short, once this weapon took the field, no thickness of armor could deliver peace of mind to those driving tanks, defending bunkers, or sailing battleships. Warships built today carry hardly any armor compared with their World War II predecessors, simply because there's no point.
Shaped charges depend on high explosives that detonate supersonically, so the first discoveries of this phenomenon occurred only after researchers had access to guncotton. Isolated experiments gave some hint of extraordinary developments, and quite a few physicists spent many years leading up to World War II wrestling with it. In 1884 Max von Foerster, then head of a nitrocellulose factory in Walsrode, Germany, was the first to publish his observations about how shaped charges could create directed energy. This was stage one, the discovery of the unlined “hollow charge.”
Five years later Charles E. Munroe, a chemist at the Newport, Rhode Island, Torpedo Station, described the surprising results of an 1887 experiment in which he had touched off a billet of hollowed guncotton sitting atop plate armor. Afterward he found the steel imprinted with a mirror image of "USN 1884," a production code that had been molded into the block of explosive and coincidentally placed against the metal. Realizing that the inscription's cavity had focused the blast, Munroe immediately began carving and drilling more blocks of guncotton to explore the mystery. Against all common sense, scooping out some of the explosive (particularly into a conical depression) was turning what would otherwise be a big omnidirectional bang into something like a chisel.
Although fully effective shaped- charge weapons would not arrive until much later, Munroe unintentionally invented the first crude example in 1894, while doing research on riot-proof bank vaults. He wired a dozen dynamite sticks around an empty tin can, fixed a smaller bundle of dynamite on top, and then set the contraption on top of a safe. The explosion blew a hole straight through a five-inch-thick safe wall. Ten times the same amount of dynamite simply heaped atop such a strongbox would not have come close to penetrating those walls.
That single experiment might have suggested that the era of steel armor was coming to an end, but this naval chemist regarded it as little more than a scientific curiosity. Neither Munroe nor von Foerster did more than publish their results. The Westfalische-Anhaltische Sprengstoff AG (WASAG) arms manufacturer received the first patent in Germany in 1910 and filed patents in England the next year. Despite the circulation of data from the patent disclosures, no belligerent tried to apply the principle to torpedoes or artillery shells during the Great War. In the mid-1930s scientists proposed a series of erroneous theories explaining why some trials, but not all, showed extraordinary capacities to focus destructive power. Such theories included intense gas pressure, the “overlapping” of shock waves, or gas jets breaking from the explosive mass to hurl bits of solid matter.
By this time Munroe, born in 1848, was finishing up a life's work in chemistry and explosives, observing before he died peacefully at age 90 that he had survived because he liked to work alone and “was always scared.” Aptly, his death year of 1938 was the first time that weapons makers learned that shaped charges had great power to harm warships, tanks, and forts . . . so long as they emulated Munroe's tin-can safe opener of 1894.
The breakthrough came out of work by Franz Rudolf Thomanek in Braunschweig, Germany, and Henry Hans Mohaupt in Zurich. Although military secrecy makes it impossible to pin down the exact date of discovery, Thomanek was probably the first to figure out that the cavity of a hollow charge needed to be lined with solid material to create what is now known as “conical shaped charge”— the most common type of three varieties, though not necessarily the most fearsome.
Thomanek had entered the field of hollow charges (employing what the Germans call the “Neumann effect”) in 1930. After reading about a new French tank with impenetrable armor, he decided to devote his career to developing antitank weapons. At the time, only a single obscure researcher in France, one Captain Lepidi, had ever discerned the importance of a liner, and unrelated mishaps had brought his research to an end in 1893.
In February 1938, after eight years of little progress, Thomanek's break came about by chance. His assistant had been assigned to dispose of a defective explosive setup supposed to determine how shaped charges would work in a vacuum, an experiment that involved a glass vessel. The quickest and safest way to destroy the worthless but deadly gadget was to blow it up next to armor on the range. Cleaning up afterward, the assistant took a closer look and excitedly called for Thomanek, who realized that the glass wall of the vacuum flask had greatly augmented the hollow charge's power.
While Thomanek's experiments showed that copper was a good all- purpose liner, zinc, which was easier to obtain in Germany, would also work. His persistent marketing efforts brought his research to the attention of the Fiihrer and triggered a visit by the Gestapo. His company went on to manufacture millions of shaped charges for the Nazi war machine. During the war the Germans assembled the largest shaped charge of all time: the 3,700-pound Mistel warhead. Fitted into the nose of a converted Ju-88 bomber, the bomb was designed to be cast loose from a piloted airplane, then dropped onto Allied capital ships and dams, but it was used only sparingly. The Japanese worked with a smaller version—the Sakura— in kamikaze airplanes.
Beside Thomanek, the most productive prewar researcher in shaped charges was the Swiss-born Mohaupt, who conducted experiments for the French army. Before he could build an operational shaped-charge warhead, the Wehrmacht entered Paris, and Mohaupt caught a ship west and brought his ideas to Maryland's Aberdeen Proving Ground in October. After successful tests against armor in 1940, the U.S. Army licensed his idea and ordered a shaped-charge hand grenade called the M10 into production. (This came about without Mohaupt’s assistance, however, because he was barred by law from working on his own secret weapon as a foreign national. He returned to Switzerland for the duration of the war, after which he was hired by the U.S. drilling industry to adapt shaped charges for use in completing oil wells.) While Mohaupt’s three-pound hand grenade could punch a hole through two inches of armor, its deployment required a near suicidal sprint to the target. As a result, the weapons languished on the shelves. Attempts to launch a variant called the M9 warhead from rifles and machine guns didn't work either.
By late 1941 the Army had a lightweight warhead able to destroy the era's lightly skinned tanks, but it lacked a delivery system with which an infantry-man could confront an oncoming tank. Meanwhile, two American Army officers had overcome all hurdles to build a workable shoulder-fired rocket launcher. But they had no lightweight, armor-busting warhead to fire. Soon thereafter these two projects would intersect and spawn almost a half-million offspring known as bazookas.
The search for an effective shoulder- fired rocket launcher had begun long before, most notably in 1866 with the pyrotechnics manufacturer Gustavus Adolphus Lilliendahl and the one- armed whaling captain Thomas Roys, who began selling a shoulder-launched rocket system. It fired an explosive- tipped rocket intended to harpoon whales at distances up to 130 feet. In both appearance and function, the whaling rocket was a closer kin to the eventual bazooka than the solid-fueled, man-portable launch weapon developed by the rocket pioneer Robert H. Goddard during the First World War.
Unfortunately for Goddard, the Armistice came less than a week after he demonstrated his rocket, and the Army declined to proceed. After recovering from tuberculosis, Goddard shifted to liquid-fueled rocket research. But his coworker, graduate student Clarence N. Hickman of Clark University, continued in the field. (During the war, the university would support more rocket research at its Allegany Ballistics Laboratory in Rocket Center, West Virginia.) And in 1931 the Army detailed Maj. Leslie Skinner to serve as a one-man rocket research center. Skinner's program doubled with the addition of Lt. Edward Uhl, expanding again in 1940 after Hickman pointed the new National Research Defense Committee toward rocket research. Working in a basement lab at George Washington University, Uhl and Skinner progressed from a closed launcher with tremendous recoil to an open- ended tube that allowed each rocket to discharge its exhaust out the back.
Top Army Ordnance officials happened to be visiting Aberdeen in May 1942, when Skinner and Uhl were firing their prototype at a moving target. Although the launcher only mounted dummy warheads, the flame and whoosh drew their attention. Skinner gamely let them test-drive it even with its rudimentary gunsight. On his first try, Gen. Gladeon Marcus Barnes, who headed weapons research and development at Ordnance, hit the target squarely. “The other staff people fired until all our rounds were gone,” Skinner would recall. “Right there and then the Bazooka was ordered into pilot production design.” In one of the fastest procurement decisions ever, the Army contracted a few days later with General Electric for 5,000 M1 launchers, and with Edward G. Budd Manufacturing Company for 25,000 M6 rockets employing a shaped charge like that in the M9 rifle grenade.
The companies had 30 days to deliver. By 1942 much American war production happened at a sprinter's pace, but this particular job gave a new meaning to “rush order.” Working 24 hours a day, General Electric engineers spent more than two weeks building and testing a dozen prototypes before the Army approved a production model. That left eight days for a converted refrigerator factory in Bridgeport, Connecticut, to turn out the goods. The supply chain included police officers who picked up pieces at the airport, hurled them in the trunks of their squad cars, and raced to the factory. General Electric finished with 89 minutes to spare.
At first the troops dubbed it the “Buck Rogers gun” but then settled on “bazooka,” because it resembled a musical instrument of the same name that movie and radio comedian Bob Burns had improvised out of pipe. The tube was made long so that the propellant would have burned out by the time the rocket left the tube, thus avoiding injury to the operator's face by exhaust flame. The Army's publicity machine was quick to celebrate this paragon of American ingenuity: the bazooka was a miracle weapon, Ordnance chief Gen. L. H. Campbell Jr. told reporters in March 1943, enabling any GI “to stand his ground with the certain knowledge that he is the master of any tank which may attack him.”
In truth the early bazookas fell short of actual panzer-stopping power. Commanding officers, including Lt. Gen. James Gavin, reported back to Ordnance that German tanks had flattened GIs who had stood their ground. Moreover, the rush of battle easily damaged the long tube. The battery circuit wasn't reliable, many troops lacked training, and some rockets misfired or bounced off their targets. But even the early M1 models were good pillbox wreckers; after the M9A1 was available, Allied soldiers were able to disable light and medium tanks, some-times working in concert with tracked tank destroyers. All told, American companies produced 441,000 bazookas and 15 million rocket warheads.
After the bazooka appeared, the Germans fielded their own tank- busting rockets: the shoulder-fired Panzerschreck (tank terror) and the short-range, single-use Panzerfaust (tank fist). Franz Thomanek insisted after the war that these were no mere knockoffs of the M1 and M9 bazookas. (This is probably true in the case of the Panzerfaust.) In any case, most GIs who tried both German and American models agreed that the bigger German weapons inflicted more damage than their 2.36-inch-diameter counterparts.
Reacting to the competition, the Army commissioned the M20 Super Bazooka, but this did not materialize in time for World War II, even arriving a bit tardily on Korean battlefields. Task Force Smith and other American units first thrown into action against the North Korean 105th Armored Brigade found that their war-surplus M9A1 bazookas had no effect on the Russian-built T-34s. On its arrival in September 1950, however, the Super Bazooka helped turn the tide, remaining in use until the one-shot, disposable M72 Light Antitank Weapon replaced it during the Vietnam War.
The Korean War generated a separate wave of shaped-charge research and development centered at the Naval Ordnance Test Station (NOTS) near China Lake, California. Shortly after U.S. Army intelligence learned of Soviet intentions to send their new Stalin JS-3 heavy tanks to North Korea, NOTS received an order to drop everything and design a shaped-charge warhead for the new Antitank Aircraft Rocket, or ATAR. These 6.5-inch¬diameter warheads, much larger and heavier than bazooka rounds, were meant to be launched by aircraft and punch through two feet of steel. Working with Caltech engineers in Pasadena, NOTS manufactured the fuses for the first 600 warheads on a temporary assembly line of folding tables, assembled in a long hallway in one of its buildings. Other workers loaded shaped charges into test warheads on office desktops.
During this time the Soviets had fielded their own shaped-charge antitank weapon, the RPG-2, which was followed in 1961 by the now infamous RPG-7, still favored by irregulars, including the pirates of Puntland who infest the Gulf of Aden. While unguided, RPG warheads cost little and work effectively with “swarm” tactics. Pilot Mike Durant, whose experiences in 1993 over Mogadishu were described in Black Hawk Down, observed how RPG smoke trails were invisible in the dust of battle at low altitudes. But the impact of the rocket on his gunship's tail was unmistakable: “It’s like hitting a speed bump when you're going fast,” he wrote. “A jarring effect.”
And now diabolically improved shaped-charge warheads are coming onto the RPG market. The “tandem” charge, for instance, employs a first charge to blow away defenses before a second takes on the armor beneath. Modern tanks rely on a series of defensive gadgetry to minimize damage from RPGs, including armor plates sandwiched with superhard ceramic; “reactive armor,” or thin packs of explosives plastered on the side of a tank, which explode to disrupt the metal jet; and rows of slats designed to damage the warheads' fuzing mechanisms.
Surprisingly, given the importance of its military applications, the vast majority of shaped-charge explosives manufactured each year are dedicated to civilian uses. David Leidel, senior scientific advisor for Halliburton/Jet Research Center in Alvarado, Texas, estimates that the oil and drilling industry consumes at least 20 million charges per year to poke numerous holes in the lower reaches of oil wells after casings are set to permit oil and gas through. The mining industry has developed conical shaped charges that can tolerate downhole temperatures of 450°F with-out detonating prematurely, need only a few teaspoonfuls of explosive, and can drill a hole through a half inch of steel, a layer of cement, or several feet of rock.
Shaped charges also serve in demolishing steel structures, mining and geophysical research, separating spacecraft stages, and hypervelocity research. Had one experiment in December 1946 been able to verify its results, the United States might well have been able to claim the first artificial satellite: one or more chunks of metal launched into orbit from a shaped charge detonated at the upper reaches of a V-2 rocket's trajectory.
The linear shaped charge, a sort of explosive rope draped or glued on a target, cuts through steel beams and opens yawning holes in concrete walls. “It forms something like a knife blade,” says Prof. Paul Worsey of the Missouri University of Science and Technology in Rolla, explaining that the V-shaped liner is forced together by the long explosive, creating a copper cutting edge that moves at hypersonic velocity. “It slaps together and welds first at the apex. It's thicker than a steak knife.”
The latest shaped charge, the explosively formed penetrator (EFP), relies on explosives packed behind a shallow metal dish to forge and launch a fast, dense cylinder of solid metal. American troops in Iraq dread the EFP's ability to disable even the heaviest tanks in the U.S. inventory. The weapon's dish, often the size of a pizza pan, delivers so much kinetic energy that the cylinder either smashes through vehicle armor or bursts with a grenadelike force inside from metal splintered off the interior of the vehicle's own armor. Unlike conical and linear shaped charges, which are aerodynamically unstable and therefore limited in range to a few inches or feet, an EFP can destroy targets at a hundred yards or more. Researchers have even designed EFPs to emerge from a blast complete with little aerodynamic fins in the back.
While the EFP remains a major threat, the greatest danger tanks face today, says Professor Worsey, could be the “long rod penetrator,” a fast-moving, dense, metallic second cousin to the EFP that strikes home as a cylindrical kinetic energy weapon, but with greater mass and force. New defensive techniques, perhaps employing sideways- sliding armor plates powered by their own explosive charges, will be required to handle it.
Shaped-charge researchers of the future will be designing multiple-shaped charges, which could simultaneously explode from the nose of a massive, earth-penetrating bomb. Designers would also like to see less liner metal wasted in the slow-moving slug and more crammed into the truly effective, fast-moving jet. While the oil industry has experienced some success by using powdered metal instead of a sheet- metal liner, perforating charges continue to consume most of the linger metal on slugs. This is not just a problem of wasted energy. The slug, which scatters its metal residue across the channel just cut by the jet, can interfere with the free flow of oil and gas into a well. With that problem in mind, engineers are investigating a significantly different type of shaped- charge liner using chemically reactive materials, which might reduce fouling, and could also show up in military applications.
More than 120 years after von Foerster and Munroe first recorded this surprising phenomenon, much of the mystery of the shaped charge is gone, but many questions remain. What are the upper limits of this otherworldly power, as explosive chemistry progresses and as computers get smarter? Will experimenters develop a fourth type of shaped charge, and if so, will that innovation turn to peaceful or warlike purposes? This Victorian-age scientific curiosity shows no sign of obsolescence.