The tunnel threat, the unknowingness of it, has eclipsed the threat of rockets in Israel’s war with Gaza. This may change in the future, if detection methods improve. For now, though, after narrowly thwarting a mega-attack in the Eshkol region on Thursday, Israel has sent in troops to find, probe, and destroy the underground arteries that stretch beneath the border, all along the border.

Conversations with current and former officers illustrate some of the challenges those forces now face in Gaza.

Brig. Gen. Miki Edelstein, the Gaza division commander, told reporters near an offensive tunnel discovered in October 2013 that the entrance to that tunnel was likely in the back yard of a civilian’s home in Rafah.

Brig. Gen. (res) Shimi Daniel, a former commander of the combat engineering corps, painted a more complex picture. He said Thursday on Channel 2 news that the entrance shafts of the tunnels are located within civilian homes and that, by the time troops arrive, “they’ve already poured fresh concrete over the opening.”

An IDF flare illuminating the sky above the Gaza strip on July 18, 2014. (Photo credit: AFP/Mahmud Hams)

An IDF flare illuminating the sky above the Gaza strip on July 18, 2014. (Photo credit: AFP/Mahmud Hams)

Once detected, soldiers from the SAMUR unit, specializing in counter-tunnel operations, lower a robot into the shaft. Major Ido, the commander of the combat engineering special forces school, said in a phone interview several months ago that the robots can send back video to the squad on the ground and have the capacity to map the contours of the tunnel.

Afterward, the army will usually send explosive-detecting dogs from the Oketz unit into the channel. On Thursday, an Oketz soldier was lightly wounded and a dog was killed in the tunnel near Kibbutz Sufa. Ordinarily, if the dog detects explosives a bomb disposal robot can be summoned.

Only then are the troops lowered into the darkness. Some of the recently discovered tunnels have been more than 60-feet-deep and over a mile long. Many have branched out near the border, with multiple exits, so as to enable a more complex attack. The army has discovered at least eight and reportedly as many as 30 offensive tunnels, thus far, and the channels are now, the army says, “under comprehensive investigation. ”

Destroying them, Major Ido said, is much easier than detecting them, but it is still difficult.

IDF soldiers stand outside the entrance to a Hamas tunnel on Friday, July 18, 2014. (photo credit: IDF Spokesperson)

IDF soldiers stand outside the entrance to a Hamas tunnel on Friday, July 18, 2014. (photo credit: IDF Spokesperson)

The tunnels can be struck from above. Brig. Gen. (res) Asaf Agmon, the head of the Fisher Institute for Air and Space Strategic Studies and a former air force pilot and commander, said the concrete-reinforced tunnels are readily penetrated by a standard one-ton bomb dropped from a plane. The fuse on the bombs, he said, simply needs to be set further back so that the bombs detonate only after penetrating into the void of the tunnel. “Bunker-busters are not necessary,” he said.

A former commander of the combat engineering corps, though, said that the destruction inflicted by air force ordnance was very “local” and did not cause dramatic damage. In order to completely dismantle a tunnel system, heavy drilling equipment has to be brought to the tunnel and many hundreds of pounds of explosives have to be inserted into the channel all along its length, he asserted.

This final stage is particularly dangerous, as the drillers are visible from afar and the explosives are perilous to transport within a combat zone. Cpt. Aviv Hakani, the Southern Command’s first counter-tunnel officer, lost his life, along with four other soldiers, while travelling toward a tunnel in the Gaza Strip in an APC that was filled with explosives and then hit by an anti-tank missile. That May 2004 incident produced the awful footage of soldiers on hands and knees in the sand along the Philadelphi Route, between Gaza and Egypt, searching for body parts – the very picture that signaled the beginning of the end of Israel’s presence in the Gaza Strip.

The current operation, which is both meant to neutralize the tunnel threat and serve as leverage during the search for a ceasefire formula, should take, from a technical perspective, two weeks, officers said.

Prime Minister Benjamin Netanyahu, in addressing the nation on Friday, the first day of the ground operation, warned that “there is no guarantee of 100% success, but we are doing our utmost in order to achieve the maximum.”

A Hamas tunnel, photographed by Israeli soldiers on Friday, July 18, 2014. (photo credit: IDF Spokesperson)

A Hamas tunnel, photographed by Israeli soldiers on Friday, July 18, 2014. (photo credit: IDF Spokesperson)