In Iraq, new ways to kill, and to counterMOSUL, Iraq In a deadly game of technological one-upmanship, insurgents have been adapting their most effective weapon, a concealed and remotely detonated bomb, to increasingly sophisticated American attempts to detect the devices before they explode.
During a morning security sweep of city streets on Thursday, American soldiers based here at Camp Freedom said the modifications suggested that there was a kind of technical elite, sometimes referred to generically as "the bomb makers," who were guiding the changing designs.
"It's this constant chess match," said Captain J. Philip Ludvigson of the Stryker Brigade, named for the nimble armored vehicle that made the sweeps. "They change their techniques around and find out new ways to kill us, and we figure out new ways to counter it."
The test of wits is important in itself, expressing itself in lives gained and lost. But soldiers involved in detecting and analyzing the devices said the game may also be providing new insight into the mysterious, dedicated and skilled core of people who may be leading the insurgency, with devastating effect across Iraq.
"The education level of the ordinary Iraqi is not sufficient to be able to initiate these things," said Captain Kenneth Mitchell, commander of the Stryker Brigade's engineer company.
"I couldn't build one of these," Mitchell said. "They are smart. There is a training network out there. There is an instructor."
Alongside that dark assessment, though, is a new sense that many of the operations involving the bombs also rely on a kind of local contractor force that is much less committed to the cause of terror than the leaders.
Those contractors are unlikely to have more expertise than the ability to take apart a garage door opener or a two-way radio - the kinds of devices used to detonate the bombs remotely - and put it back together again, but this time connected to a blasting cap.
Others, especially those who put the bombs in place, are simply laborers without any specialized knowledge or much motivation when it comes to committing terrorist acts.
"In some cases I feel straight up that the guys are just making money," said Captain Robert Cope, an expert on destroying unexploded bombs in the 744th Ordnance Company. "They see that their devices are not working properly and they don't modify it."
For months, private and governmental threat reports have listed the bombs, referred to generically as "improvised explosive devices," as the prime threat to Western military and civilian convoys.
In Mosul, a senior military officer said, 40 to 50 percent of the 778 attacks so far this year have been the result of such bombs. Although there are also large numbers of mortar attacks, that method is notoriously inaccurate and much less lethal than the remotely detonated bombs, which an assailant can explode as a target passes.
The bombs generally involve a blasting cap, detonated by an electric current by something as simple as a cordless phone, a garage door opener or a remote-controlled toy. The cap may detonate a plastic explosive that has been placed into the nose of a mortar round. When the round explodes, it may set off other shells or plastic explosives placed near it.
Explosives experts here said that the earliest devices often had wires running from a porch or a house to the bomb, making it easy to trace the perpetrator. Later the remote-controlled bombs became more common.
The ways in which the bombs have been concealed has also become more sophisticated. Recently, soldiers said, bombs have been disguised as curbing on the side of the road.
The explosives inside have also evolved. In just the last few weeks, insurgents have for the first time tried to explode bombs with a kind of homemade napalm that is called fougasse, a concoction of gasoline and detergent.
The Americans use electronic jamming to disable some of the bombs, but those methods are largely considered secret and not discussed openly by soldiers.
During the sweep on Thursday, one soldier, Sergeant Benjamin West, peered at a television screen in one of the vehicles, switching back and forth from visible to infrared imagery in a search of the streets for suspicious objects.
Three more soldiers - Staff Sergeant Robert Renfro, Sergeant Nathan Francis and Specialist Joshua Donoho - stood looking out hatches in the top of the Stryker vehicle, watching for anything suspicious.
However technologically advanced the battle becomes, eyes and ears are still the first line of defense against the bombs, said Brigadier General Carter Ham, commander of the American-led forces in northern Iraq, which have their headquarters at Camp Freedom.
"If there's a trash can where there's not normally a trash can, then they'll investigate that," he said.