For weeks he’d been visiting beauty supply stores, filling his carts with hydrogen peroxide and nail polish remover. At the Beauty Supply Warehouse, among the rows of wigs, braids, and extensions, the manager knew him as Jerry. He said his girlfriend owned hair salons. There was no reason to doubt him.

On pharmacy shelves, in the little brown plastic bottles, hydrogen peroxide is a disinfectant, a sting-free way to clean scrapes. Beauty salons use a more concentrated version to bleach hair or activate hair dyes. At even higher concentrations, it burns the skin. It is not flammable on its own, but when it reacts with other chemicals, it quickly releases oxygen, creating an environment ripe for explosions. . . . Even with a cheap stove, it’s easy to simmer water out of hydrogen peroxide, leaving behind something more potent. It takes time, and he had plenty of that.

Preparing the explosive initiator was only slightly more complicated, but considerably more dangerous. Hence, Zazi had to be especially careful. “He added the muriatic acid and watched as the chemicals crystallized,” the account continues:

The crystals are known as triacetone triperoxide, or TATP. A spark, electrical current, even a bit of friction can set off an explosion. . . .

The white crystal compound had been popular among Palestinian terrorists. It was cheap and powerful, but its instability earned it the nickname “Mother of Satan”. . . .

When he was done mixing, he rinsed the crystals with baking soda and water to make his creation more stable. He placed the finished product in a wide-rimmed glass jar about the size of a coffee tin and inspected his work. There would be enough for three detonators. Three detonators inside three backpacks filled with a flammable mixture and ball bearings—the same type of weapon that left 52 dead in London in 2005. . . .

He was ready for New York.

These types of improvised weapons are not only devastatingly effective but also remarkably inexpensive, further accounting for their popularity. For example, the House of Commons Intelligence and Security Committee, which investigated the 2005 London transport attacks, concluded that the entire operation cost less than £8,000 to execute. This sum included the cost of a trip to Pakistan so that the cell leader and an accomplice could acquire the requisite bomb-making skills at a secret Al Qaeda training camp in that country’s North-West Frontier Province; the purchase of all the needed equipment and ingredients once they were back in Britain; the rental of an apartment in Leeds that they turned into a bomb factory; car rentals and the purchase of cell phones; and other incidentals.

The cost-effectiveness of such homemade devices—and their appeal to terrorists—is of course not new. Decades ago, the Provisional Irish Republican Army (PIRA) demonstrated the disproportionate effects and enormous damage that crude, inexpensive homemade explosive devices could achieve. In what was described as “the most powerful explosion in London since World War II,” a PIRA fertilizer bomb made with urea nitrate and diesel fuel exploded outside the Baltic Exchange in April 1992, killing three people, wounding ninety others, leaving a twelve-foot-wide crater—and causing $1.25 billion in damage. Exactly a year later, a similar bomb devastated the nearby Bishops Gate, killing one person and injuring more than forty others. Estimates put the damage of that blast at $1.5 billion.

Long a staple of PIRA operations, in the early 1990s fertilizer had cost the group on average 1 percent of a comparable amount of plastic explosive. Although after adulteration fertilizer is admittedly far less powerful than plastic explosives, it also tends to cause more damage than plastic explosives because the energy of the blast is more sustained and less controlled.

Similarly, the homemade bomb used in the first attack on New York’s World Trade Center in 1993—consisting of urea nitrate derived from fertilizer but enhanced by three canisters of hydrogen gas to create a more powerful fuel-air explosion—produced a similarly impressive return on the terrorists’ investment. The device cost less than $400 to construct. Yet, it not only killed six people, injured more than a thousand others and gouged a 180-foot-wide crater six stories deep, but also caused an estimated $550 million in damages and lost revenue to the businesses housed there. The seaborne suicide-bomb attack seven years later on the USS Cole, a U.S. Navy destroyer anchored in Aden, Yemen, reportedly cost Al Qaeda no more than $10,000 to execute. But, in addition to claiming the lives of seventeen American sailors and wounding thirty-nine others, it cost the U.S. Navy $250 million to repair the damage caused to the vessel.

THIS TREND toward the increased use of IEDs has had its most consequential and pernicious effects in Iraq and Afghanistan during our prolonged deployments there. As Andrew Bacevich, a retired U.S. Army officer and current Boston University professor, has written, “No matter how badly battered and beaten, the ‘terrorists’” on these and other recent battlefields were not “intimidated, remained unrepentant, and kept coming back for more, devising tactics against which forces optimized for conventional combat did not have a ready response.” He adds, “The term invented for this was ‘asymmetric conflict,’ loosely translated as war against adversaries who won’t fight the way we want them to.”

In Iraq and Afghanistan, both terrorists and insurgents alike have waged low-risk wars of attrition against American, British, allied and host military forces using a variety of IEDs with triggering devices as simple as garage-door openers, cordless phones and car key fobs to confound, if not hobble, among the most technologically advanced militaries in the history of mankind. “The richest, most-trained army got beat by dudes in manjammies and A.K.’s,” an American soldier observed to a New York Times reporter of one such bloody engagement in Afghanistan five years ago.

Indeed, terrorists and insurgents in both Afghanistan and Iraq have demonstrated the effectiveness of even poorly or modestly armed nonstate adversaries in confronting superior, conventional military forces and waging a deadly war of attrition designed in part to undermine popular support and resolve back home for these prolonged deployments. Equally worrisome, these battle environments have become spawning grounds for continued and future violence: real-life training camps for jihadis and hands-on laboratories for the research and development of new and ever more deadly terrorist and insurgent tactics and techniques. “How do you stop foes who kill with devices built for the price of a pizza?” was the question posed by a Newsweek cover story about IEDs in 2007. “Maybe the question is,” it continued, “can you stop them?”

At one point, IEDs were responsible for nearly two-thirds of military fatalities caused by terrorists and insurgents in Iraq and a quarter of the military fatalities in Afghanistan. According to one authoritative account, there was an IED incident every fifteen minutes in Iraq during 2006. And, after the number of IED attacks had doubled in Afghanistan during 2009, this tactic accounted for three-quarters of military casualties in some areas.

These explosive devices often were constructed using either scavenged artillery or mortar shells, with military or commercial ordnance, or from entirely homemade ingredients. They were then buried beneath roadways, concealed among roadside refuse, hidden in animal carcasses or telephone poles, camouflaged into curbsides or secreted along the guard rails on the shoulders of roadways, put in boxes, or disguised as rocks or bricks strewn by the side of the road. As military vehicle armor improved, the bomb makers adapted and adjusted to these new force-protection measures and began to design and place IEDs in elevated positions, attaching them to road signs or trees, in order to impact the vehicles’ unarmored upper structure.

The method of detonation has also varied as U.S., allied and host forces have adapted to insurgent tactics. Command-wire detonators were replaced by radio-signal triggering devices such as cell phones and garage-door openers. These devices were remote wired up to one hundred meters from the IED detonator to obviate jamming measures. More recently, infrared lasers have been used as explosive initiators. One or more artillery shells rigged with blasting caps and improvised shrapnel (consisting of bits of concrete, nuts, bolts, screws, tacks, ball bearings, etc.) have been the most commonly used, but the makeshift devices have also gradually become larger as multinational forces added more armor to their vehicles, with evidence from insurgent propaganda videos of aviation bombs of 500 lb. being used as IEDs. In some cases, these improvised devices are detonated serially—in “daisy chain” explosions—designed to mow down quick-reaction forces converging on the scene following the initial blast and first wave of casualties.

By 2011, the U.S. Defense Department had spent nearly $20 billion on IED countermeasures—including new technologies, programs, and enhanced and constantly updated training. A “massive new military bureaucracy” had to be created to oversee this effort and itself was forced to create “unconventional processes for introducing new programs,” as a 2010 New America Foundation report put it. Yet, as the British Army found in its war against Jewish terrorists in Palestine seventy years ago, there is no easy or lasting solution to this threat. IED attacks had in fact become so pervasive in Palestine that in December 1946 British Army headquarters in Jerusalem issued a meticulously detailed thirty-five-page pamphlet, complete with photographs and diagrams, describing these weapons, their emplacement and their lethal effects. Even so, as military commanders and civilian authorities alike acknowledged at the time, IEDs were then as now virtually impossible to defend against completely.

Image: Pullquote: As mesmerizingly attractive as nonconventional weapons remain to Al Qaeda and other terrorist organizations, they have mostly proven frustratingly disappointing to whoever has tried to use them.Essay Types: Essay