From a recent STRATFOR Security weekly post, By Scott Stewart:

Sunday will mark the 15th anniversary of the 9/11 attacks, and it is incredible to think how much time has passed since that day. Like so many traumatic events, 9/11 has imprinted in most people’s minds where they were and what they were doing when two airliners struck the twin towers of the World Trade Center that once dominated the New York City skyline and a third jet hit the Pentagon. In the weeks that followed, it was not uncommon to hear people say things like “the attacks changed everything” and “nothing will ever be the same.” A sense of patriotism spread across the United States, and foreign leaders declared that the whole world was American. But in the years since, human nature and entropy have shown how fleeting such sentiments can be.

One of the things that 9/11 supposedly changed forever was the United States’ approach to national security and counterterrorism. Billions of dollars were spent to build vast new bureaucracies like the Department of Homeland Security and the Office of the Director of National Intelligence. Billions more have been spent to prosecute the still-unfinished war on terrorism, which has spread from Afghanistan and Iraq to Yemen, Libya and Syria. But like the swell of patriotism and global unity, the security lessons of 9/11 will be lost to the fog of time if they are not carefully heeded.

Sophisticated Tradecraft Is Not Dead

Before the 9/11 attacks, al Qaeda had amassed an impressive array of terrorist planners, trainers and training camps. Figures such as Khalid Sheikh Mohammed, Mohammed Atef and Abu Zubaydah were available to instruct the group’s fighters in a variety of terrorist tradecraft skills, including how to travel to and operate in hostile environments, covertly finance operations, compartmentalize cellular operations and clandestinely communicate. Many of these skills were employed on 9/11, and though there were some gaffes that could have blown the operation, the terrorists’ level of proficiency was enough to get the job done. The training camps also gave al Qaeda leaders a chance to become acquainted with the recruits who passed through them, selecting some for special missions — including potential pilots and hijackers who were likely to be successful in obtaining U.S. visas — and training them accordingly.

In the wake of the 9/11 attacks, the United States and its allies relentlessly hunted down and killed or arrested most of al Qaeda’s cadre of planners and trainers. They also disrupted the group’s financing and coordination networks, in part by killing Osama bin Laden and his primary communications cutout, Atiyah Abd al-Rahman. While targeting al Qaeda’s core, the U.S.-led coalition began dismantling local franchise groups as well, resulting in the detention or deaths of more jihadists who possessed a high degree of tradecraft.

Many parts of the al Qaeda movement, including its core and several franchises such as the Iraqi node (which eventually became the Islamic State), began to find it increasingly difficult to operate deep inside hostile territory like the continental United States. Instead, they began to promote the idea of leaderless resistance among their followers in an effort to continue attacking tougher Western targets. But though the switch to grassroots terrorism made it possible to strike at the heart of the group’s enemies, it came at a price: The same isolation that enhances operational security for grassroots jihadists also makes it extremely difficult for them to get training.

It is no surprise, then, that many recent terrorist attacks have not demonstrated the type of tradecraft seen in the 9/11 attacks. Even the deadly assaults on Paris in November 2015 and on Brussels in March, which were directed by the Islamic State’s external operations branch in Syria, showed significant shortfalls in planning and execution.

This does not mean, however, that sophisticated tradecraft is dead, or that groups and individuals cannot develop and use it in future attacks. The poor preparation and delivery exhibited by most jihadists today cannot be allowed to lull security forces into complacency, only to be caught off guard by advanced operatives tomorrow. Amateur jihadists frequently stumble into FBI sting operations, but professional terrorists are not as easy to snare. More important, tradecraft was neither the only nor the primary reason that the 9/11 attackers were so successful.

Patterns Can Be Changed

The critical component of the 9/11 attack was the perpetrators’ conceptualization and planning. Typically, terrorists will try to amass the explosive material for a large bombing, the weapons for an armed assault, or the ingredients for multiple small bombs. But rather than take the traditional approach, Khalid Sheikh Mohammed adopted an outside-the-box strategy. He decided to use an improvised weapons system that was part of the United States’ infrastructure — air transportation — to attack the nation itself. Airlines have long been considered a prime terrorist target, but instead of viewing them as targets alone, Mohammed thought to use them as human-guided cruise missiles.

Such an imaginative approach to the problem of conducting a mass casualty attack required more than just a novel idea and a set of skills. It also required a deep understanding of the U.S. air transportation system, including airport security screening measures and the emergency protocols followed by pilots and crews in a hijacking. With this detailed knowledge, Mohammed knew that razor blade boxcutters — the weapons his hijackers used — were permitted aboard aircraft. Some reports suggest that the 9/11 attackers also used fake suicide bombs crafted from items allowed onboard to coerce the aircraft’s crews and passengers into meeting their demands.

Mohammed exploited his knowledge of emergency procedures to plan the execution of the attack, too. Before 9/11, aircraft crews were trained not to resist hijackers but to comply with their instructions in an effort to calm the situation and land the plane. Once the aircraft was on the ground, hijackers would then either surrender or be killed by an aircraft entry team. The Federal Aviation Administration never dreamed that terrorists would commandeer an aircraft with the intent to use it as a weapon. Aware of this, the 9/11 attackers simply had to pretend to be typical hijackers to gain the crews’ cooperation and take control of the aircraft. Mohammed and his comrades were thus able to operate within the rules of the system and turn it against the country that had created it in the first place.

But the advantage Mohammed gained by shifting the hijacking paradigm was short-lived, as evidenced by the events that unfolded that morning aboard the fourth aircraft: United Airlines Flight 93. The attackers who targeted the plane did not account for the fact that its passengers and crew were able to use their cellphones to talk to people on the ground. When they learned what had happened to the three other aircraft, they revolted and forced the hijackers to crash the plane before it could be used to target the U.S. Capitol.

Nevertheless, security protocols changed dramatically after 9/11 in an effort to keep history from repeating itself. Cockpits were hardened, passenger screening became more intensive, the number of federal air marshals increased, and pilots were permitted to travel with weapons. Perhaps the most important adjustment, though, was the change in mindset that occurred among aircraft crew and travelers. Hijackers can no longer coerce pilots, crews or passengers to surrender control of an airplane with the threat of force alone.

In response to this new reality, terrorist planners have reverted to their former view of aircraft as targets. Starting in December 2001, a string of attacks has been conducted against aircraft using shoe bombs, liquid bombs and underwear bombs. More recently, Metrojet Flight 9268 was bombed after leaving Egypt’s Sharm el-Sheikh airport in November 2015, and attackers attempted to bomb Daallo Airlines Flight 3159 in Mogadishu in February.

Crossing the Next Rubicon

Mohammed’s innovative concept did not have a long shelf life, but that did not stop it from proving destructive and deadly. Furthermore, he was not the first terrorist to shift the paradigms we’ve come to know by launching an unprecedented attack — nor will he be the last. This will be important to keep in mind as security forces focus on identifying and thwarting plots by amateur grassroots jihadists. Though these terrorists, armed with bombs and guns, can certainly cause death and mayhem, it is rarely on the scale seen during 9/11. Attempts to catch them, therefore, should not detract from intelligence and law enforcement efforts to detect and prevent plots conducted by professional, innovative operatives that could have truly catastrophic consequences.

To guard against such plots, government officials, private industry leaders and security directors need to work together to identify vulnerable nodes of national infrastructure that could be used as weapons, as the air transportation system was. They must examine the security policies, procedures and patterns that a clever terrorist could exploit and then take steps to address those weaknesses. Creativity is not just needed to plan professional terrorist attacks; it is also needed to craft the security measures that defend against them.