THE “hell cannons” of Aleppo pack a deadly punch. Cobbled together in Syria by militant groups fighting to overthrow the autocratic regime of Bashar al-Assad, they use an explosive charge at the bottom of a pipe to hurl a propane cylinder crammed with 40kg or more of explosives and shrapnel. A finned tail welded to the cylinder shields it from the launch blast and provides stability in flight. The Ahrar al-Sham brigade reckon the cannons can hit targets 1.5km away. Fuses detonate the cylinder upon impact or, using a timer, after it punches into a building. This is all the better to demolish several floors with a single strike.

The use of improvised weapons in conflict has a long and bloody history: from the Irish shillelagh, a walking stick that doubles as a club—especially effective when the knob at the top is loaded with lead—to the Molotov cocktail, as the glass petrol bombs the Finnish army hurled at Russian tanks during the second world war came to be known.

The modern equivalents are more high-tech and, like Aleppo’s hell cannons, far deadlier. This comes from a combination of more sophisticated and easily available “off-the-shelf” equipment, and the internet providing a ready medium to spread new weapon-making ideas. The upshot is a reshuffling of the cards in modern warfare, says Yiftah Shapir, a weapons expert at Tel Aviv University and a former lieutenant colonel in Israel’s air force. Any side that begins with a technological advantage will see it erode quickly as the underdogs improve their improvisation capabilities.

The ominous consequences have led America’s Defence Advanced Research Projects Agency (DARPA), an arm of the Pentagon, to try to keep up with developments by soliciting worldwide for new ways to make weapons using commercially available materials and technologies. More than 20 experts are now reviewing hundreds of submissions. To better assess the risks, some of the most promising designs will be built as prototypes and tested. This could earn their inventors awards of up to $130,000.

Fire in the hole

The DARPA experts need to move fast. Only a few years ago the Syrian rebels were lobbing small bombs with slingshots made from lengths of rubber tubing. Now some of the hell cannons are being mounted on vehicles and fitted with recoil springs to absorb the launch explosion. This improves stability, which in turn enables greater accuracy with follow-up shots. Some designs are no longer fired by lighting a fuse, but at a safe distance with a car battery wired to the propellant charge. Bigger cannons heave oxygen cylinders and, astonishingly, even large household water-heaters packed with enough explosives to destroy a cluster of buildings.

Improvised weaponry typically is not as fearsome as that made by defence companies. But it is a lot cheaper and often effective enough, says Vincent Desportes, formerly a general in the French army and a military attaché to the United States. Despite receiving arms shipments from Iran and Russia, Syria’s regime still uses its own improvised “barrel bombs”—devastating devices made by filling oil drums with explosives and scrap metal. Hizbullah, a Lebanese militia fighting to keep Mr Assad in power, also weaponises non-military materials. The group uses Google Earth to find and hit targets with rockets more accurately, adds Mr Shapir.

Even defence firms are turning to more commercially available equipment to make weapons. Lasers used to cut and weld materials in industry, for example, are now so powerful that Boeing bought a 10kW model to put into its High Energy Laser Mobile Demonstrator (HEL MD), a system it has assembled for the American army to shoot down drones and incoming mortar shells by firing a laser beam at them. Just think of HEL MD as “a welding torch” with a reach of kilometres, says David DeYoung, head of the Boeing unit that built it. While the off-the-shelf laser is powerful enough for its role, IPG Photonics of Massachusetts is now selling a 20kW laser.

Smartphones are useful in making weapons. They contain GPS navigation and frequency-hopping technology, which transmits signals that are hard to intercept or jam (both were military developments). Other useful things inside include accelerometers, compasses, gyroscopes, motion detectors and sensors for orientation, measuring magnetic fields and capturing reflected infra-red light (to turn off the screen when it detects the phone is close to the ear, saving battery power and preventing inadvertent touches). All of that can be used for missile guidance and communications, adds Mr Shapir. The guidance and remote-control systems sold with consumer drones offer additional capabilities.

Some of the improvised weapons suggested to DARPA are highly advanced, says John Main, head of Improv, as the agency’s programme has been named. Once Improv’s own analysis of the proposals is complete DARPA may make some of the plans publicly available to raise awareness of potential risks. Two decades ago, assessing threats from an adversary involved getting ten experts in a room for a few days. Now, says Mr Main, thanks to the profusion of information and readily available advanced technologies, we need “a very, very large ‘red team’” of hundreds of outside technologists to brainstorm the types of attacks that might be concocted.

Part of the problem is that anyone can buy not just sophisticated hardware but also a 3D printer to make basic weapon components, says Rear-Admiral Brian Brakke, deputy director of operations at the Pentagon’s Joint Improvised-Threat Defeat Agency. In Iraq and Syria, Islamic State has been working on dropping improvised bombs from remotely controlled model aircraft. These might carry bigger payloads than the small quadcopters widely sold as drones to hobbyists and commercial operators. The jihadist group has also begun developing remote-control systems for driverless vehicles to deliver huge improvised explosive devices without suicide-volunteers, Mr Brakke believes.

Of considerable concern is that many manufacturers of improvised weapons may not respect bans on devices deemed by many nations to be beyond the pale. Some of the barrel bombs being dropped by Syria’s air force contain chlorine, an ingredient prohibited by the 1997 Chemical Weapons Convention.

The new minefield

Half a century of conflict has left the Colombian countryside littered with improvised mines. Many have been fashioned by FARC guerrillas without the use of any metal, which is prohibited by a 1996 international convention because the devices cannot be found with metal detectors. Some rely on pressure from a foot pushing down on a syringe which squirts a reactive agent into a glass jar filled with explosive, says Camilo Serna Villegas, chief technologist with the Colombia Campaign to Ban Landmines, an NGO based in Bogotá. With peace efforts now in progress, FARC and government forces have begun clearing some minefields, but it is a painfully slow process that can involve ground being searched by hand.

The risk of nasty biological attacks has risen, too. Commercial drones used for spraying new biopesticides derived from natural materials could be adapted to spray more sinister stuff, says Piers Millett, a former deputy head of the United Nation’s implementation team for the Biological Weapons Convention.

Recent developments in biotechnology have moved the boundaries as well. So-called “biohacking” groups have begun experimenting with homespun processes, much as early computer hackers did with information technology. The biohackers see DNA as a form of software that can be manipulated to design new biological processes and devices. Some of the amateur labs are still relatively crude, but nevertheless there is concern that they could be used to create killer bugs or provide training for bioterrorists. America’s FBI has been watching developments and even organising some biohacker gatherings. That may seem reckless, but the idea is to encourage responsible behaviour and self-policing rather than risk a crackdown that drives the movement underground.

The array of deadly things that can now be improvised with modern materials and technologies is terrifying. At least knowing what is possible will provide some idea of where the dangers now lurk. That, in turn, should help deliver some defence against the weapons-improvisers.