When Ramadi fell to the Islamic State in May, initial reports were that the terror group used a complex series of massive car bombs to overwhelm the remaining Iraqi Security Forces inside the city.
It may have used another tactic too, one that’s gained renewed attention by U.S. airstrikes: a complex network of underground tunnels used to move forces and equipment, and in Ramadi’s case, potentially plant a devastating bomb.
“We do see tunneling as a technique that Daesh uses,” said U.S. Marine Corps Brig. Gen. Thomas D. Weidley, chief of staff of Combined Joint Task Force — Operation Inherent Resolve.
“We see them use it not only to move equipment and fighters but we also see them used as IEDs — if you will, a tunnel IED — and I think we saw that in Ramadi earlier,” he said. “So wherever we can find these tunneling activities we will look to strike them.”
On June 15, the Department of Defense reported a set of targets in its daily airstrike report: two Islamic State “tunnel systems” in Syria, a tunnel entrance and two additional tunnel systems in Iraq. A spokesman for Operation Inherent Resolve said that since airstrikes began, U.S. and coalition aircraft have hit 28 tunnels in 22 airstrikes, although he could not elaborate further for reasons of operational security.
In recent months, the Pentagon has characterized its progress against the Islamic State in terms of how the terror group can no longer complete large, uncontested ground movements without getting hit by coalition airpower.
It’s not clear how much of the movement by the terror group through the tunnels is an adaptation to air dominance by the coalition, or how much of its movements are now conducted through tunnels.
But tunnels were a common threat in the initial 2003 combat operations in Iraq, where forces loyal to Saddam Hussein were caught in vast tunnel systems connecting strategic targets to cities, such as the network found under Baghdad International Airport and at Tallil.
That more than a decade later they are still used by the Islamic State as a strategic way to move fighters and equipment beyond the view of U.S. air assets underscores how difficult it is for U.S. and coalition aircraft to target them.
“We’d see them used in Southern Iraq, we’d see Shi’a militias use them to move around inside cities, because they are in such close proximity to the civilian population its not something we were willing to target,” said Chris Harmer, a former Navy helicopter pilot who is now a senior analyst at the Institute for the Study of War.
Harmer said the often hand-dug tunnels show why an air campaign is not going to defeat the Islamic State.
“I do think we should be striking ISIS’ tunnels. They’re used to store weapons and ammunition,” he said. “They need to be destroyed. But you can’t win a war from 30,000 feet bombing six guys in a tunnel.”
