Israelis have been aghast at the scope of the Trojan-horse-like network of tunnels built by the hardline Islamists in the Gaza Strip and revealed to their horrified gaze during Operatio Protective Edge.

These elaborate feats of engineering — complete with ventilation systems, electricity and stashes of food — allow armed Hamas fighters to strike at will, penetrating kibbutzes and other communities near the border with the Gaza Strip.

Some people are even talking of a possible “Israeli 9/11.”

There are dozens, if not hundreds, of these tunnels, explains Maj. Arieh Shalicar of the Israeli Defence Forces (IDF).

They lead “from mosque to mosque; mosque to house; house to hospital; kindergarten to house … It is estimated that gunmen are able to live inside a tunnel for weeks at a time, apparently sustained by the quantities of dates and water left behind.”

Lest there be any doubt about the tunnels’ purpose, the IDF found weapons, army uniforms and motorcycles, along with chloroform and handcuffs — a macabre “kidnapping kit.”

“Basically, a Hamas terrorist can enter one of these tunnels in civilian clothes without arms and pop up somewhere else, fully clothed in an Israeli army uniform brandishing a Kalashnikov, ready to attack someone,” says Maj. Shalicar.

Destroying the tunnels was the main objective of Operation Protective Edge. Israeli forces say they located and destroyed 32 of them, including 14 running underneath the Gaza-Israeli border.

But the structures had already proved their worth — they enabled the terrorists to ambush Israeli soldiers and led to high numbers of casualties.

Last October, IDF intelligence located entrances to an elaborate tunnel just a few hundred metres from Kibbutz Ein Hashlosha.

Users must climb down a steep slope to reach its entrance, then crawl through the deceptively small opening.

Coming from the desert’s summer heat and humidity into the coolness of a subterranean concrete-lined structure, it was surprising to find oneself able to stand erect and see far enough to sense distance — and lots of it.

Though visibility is limited by the dearth of ambient light and helped only slightly by the lighting unit attached to a reporter’s camera, the vast dimension of the expanse was perceptible, the elaborate nature of the structure striking.

Like many of Hamas’s tunnels, this one is lined with concrete and equipped with an array of cables, conduits, finished ceilings, communication lines and pulley systems. It’s estimated it took several years and millions of dollars to build — mostly by hand, using a jackhammer and shovels.

Now, Israelis are asking how the tunnels could have been constructed literally underneath their noses.

“Who knew what when?” is only the first to be directed to the Netanyahu administration. Consider as well the apparently undetected noise and dirt accompanying the construction that used scores of tons of cement — perhaps the most often-cited example of substances usually banned for delivery into the Gaza Strip since Israel initiated its blockade in 2007.

The passage of goods and people in and out of the territories is overseen by the Coordinator of Government Activities in the Territories, which answers to the Israeli Defence Ministry. Its spokesman, Guy Inbar, says building materials were barred from entering the territory after the tunnels were discovered in October. An exception was later made for programs run by the United Nations, U.S. or European organizations.

But tunnels have been part of the Gaza scene for decades. In September 1989, terror mastermind Mahmoud Al-Mahbrouh used one to evade Israeli security forces.

By the mid-1990s, they were being dug from Rafah into Egypt, big enough for children to crawl through to bring in cigarettes. The structures quickly proliferated as a black-market trade mushroomed to sidestep the Israel blockade, smuggling in just about everything customers wanted, including ammunition and other military hardware.

More recently, the tunnels became more sophisticated and complex, designed to serve as staging platforms for terror-related activities.

But the burning question remains: How do you detect the tunnels?

Although scores of proposals have been submitted to the Israeli Defence Ministry’s Administration for the Development of Weapons & Technological Infrastructure, no one has yet come up with the answer.

That’s because the technology must be dual-purpose: it must cover a wide area and be able to locate a man-sized tunnel buried more than a few metres underground, says Dr. Eado Hecht, a defence analyst for the Begin-Sadat Centre in Jerusalem.

The Hamas tunnels are usually 20 metres deep — which puts them out of range of the current technology even if the searchers have a rough idea of their location. Instead, Israel must rely its intelligence and information gathered in house-to-house searches.

In addition, destroying a tunnel is a lengthy and complex operation, says Dr. Hecht. Just blowing up the entrance or some of the airshafts leaves most of the tunnel intact, so Hamas sappers will be able to dig by-pass sections and continue to use the structure.

Therefore, the entire length of the tunnel and its branches must be located, mapped and completely destroyed.

“The Israeli Defence Forces have put a lot of effort into finding solutions,” says Amir Rappaport, editor-in-chief of Israel Defense. “[S]o far, they have a combination of a few imperfect solutions based on a lot of intelligence and other aspects to find tunnels.”

The most promising answer — which entails planting sensors in the ground — is about two years away from being usable, he says.

The technology could have major commercial applications. It could be used, for example, in the United States, where smugglers have built tunnels along the Mexican border.