Israel has uncovered an underground fortress under Gaza

One tunnel in Gaza was wide enough for a top Hamas official to drive a car into. Another stretched nearly three football fields and was hidden beneath a hospital. Under the home of a senior Hamas commander, the Israeli army found a spiral staircase leading to a tunnel about seven stories deep.

These details and new information about the tunnels, some of which have been made public by the Israeli military and documented by video and photographs, underscore why the tunnels were considered a major threat to the Israeli military in Gaza even before the war began.

But Israeli officials and soldiers who have been in the tunnels since then — as well as current and former U.S. officials with experience in the region — say the size, depth and quality of the tunnels built by Hamas have amazed them. Even some of the machinery Hamas used to build the tunnels, as seen in captured videos, has taken the Israeli military by surprise.

The Israeli military now believes there are many more tunnels under Gaza.

In December, the network was estimated to be 250 miles long. Senior Israeli defense officials, who spoke on condition of anonymity to discuss intelligence matters, currently estimate that the network is between 350 and 700 kilometers long – extraordinary figures for an area that is only 40 kilometers at its longest point. Two of the officials also found that there are nearly 5,700 individual shafts leading to the tunnels.

The figures could not be independently verified, and there are varying estimates from Israeli officials about the wider reach of the tunnel network, based on different intelligence. But Hamas's massive efforts to militarize the enclave are not in question; nor does the failure of the Israeli military's intelligence services in underestimating the size and importance of the network to Hamas's survival.

At a meeting in January 2023, a top Israeli official said the tunnels would not even be a factor in a future war with Hamas because of Israel's military strength, according to a transcript of the discussion reviewed by The New York Times.

“Hamas has spent the last 15 years turning Gaza into a fortress,” said Aaron Greenstone, a former CIA officer who has worked extensively in the Middle East.

For the Israeli army, the tunnels are an underground nightmare and the core of Hamas's ability to survive. Every strategic objective of Israel in Gaza is now linked to wiping out the tunnels.

“If you want to destroy Hamas' leadership and arsenal, you have to destroy the tunnels,” said Daphné Richemond-Barak, an expert on tunnel warfare at Reichman University in Israel. “It has become connected to every part of the military missions.”

Hamas has invested heavily in the tunnels because it does not have the resources or numbers to fight the Israeli army in a conventional war. The group uses the tunnels as military bases and arsenals, relying on them to move its troops undetected and protect its top commanders.

A 2022 document showed that Hamas had budgeted $1 million for the tunnel doors, underground workshops and other expenses in Khan Younis.

Israeli intelligence officials recently determined that there are about 100 miles (160 kilometers) of tunnels just beneath Khan Younis, the largest city in southern Gaza, where Israeli forces are now engaged in heavy fighting. Yahya Sinwar, the military leader of Hamas in Gaza, had a house in Khan Younis.

In addition, a 2015 report indicated that Hamas had spent more than $3 million on tunnels throughout the Gaza Strip, including many built under civilian infrastructure and sensitive locations such as schools and hospitals, the Israeli military said.

The Israeli military said it had found two types of tunnels: those used by commanders and others used by officers. The commander tunnels are deeper and more comfortable, allowing longer stays and use of ceramic tiles. The other tunnels are more spartan and often shallower.

An Israeli official said the army may have spent a year locating a single tunnel, but the ground campaign has now yielded a wealth of information about Gaza's underground network.

The Israeli military has examined computers used by Hamas operatives responsible for tunnel construction to find the underground passages, a senior Israeli official said. Some documents captured during the war also prove vital. The Israeli military has found lists of the families who 'hosted' the tunnel entrances in their private homes.

In one case, Israeli soldiers found a map of tunnels in Beit Hanoun, a city in northern Gaza, and used it to find and destroy tunnels. Even with this information on the battlefield, the fighting in Gaza around the tunnels has been grueling. The Israeli military reports that nearly 190 soldiers have been killed and about 240 seriously injured since the ground campaign began. But the military has not disclosed the number of deaths and injuries linked to the tunnel war.

One soldier, who spoke on condition of anonymity for security reasons, said he oversaw the destruction of about 50 tunnels in Beit Hanoun. They were all trapped, he said. The soldier, a combat engineers officer, said his unit found bombs hidden in walls and a huge explosive device wired to be activated remotely.

The soldier, who was a reservist and has since been discharged, said the device was made in a factory and had a serial number on it. If the bomb had gone off, it would have killed everyone in the tunnel and immediately outside, he said.

Hamas released a video in November showing how it lured a group of five Israeli soldiers to a tunnel entrance in Beit Hanoun and then used a roadside bomb to kill the soldiers.

Ms. Richemond-Barak said Hamas had imported the tactics of Syrian rebels who killed dozens of government troops in a tunnel attack in Aleppo in 2014.

On January 8, Israeli soldiers took journalists to view three tunnel shafts in central Gaza – one in a one-story farmhouse on the outskirts of Bureij, the second in a civilian steel mill on the outskirts of Maghazi and a third in a shed near the steel mill .

The shaft in the steel mill was the deepest and most advanced. It descended about 30 meters and was equipped with some kind of elevator. The soldiers said it was used to transport ammunition parts cast at the steel mill. A bucket of grenades or warheads lay nearby. The soldiers said the grenades were based on a template of a yellow US-made mortar round with the words “20mm mortar round; Lot 1-2008.”

The soldiers did not allow journalists into the shaft due to the risk of explosions, but said Hamas would carry the ammunition parts into the tunnel to transport them to another part of the tunnel network, where they would be fitted with explosives.

The tunnel would lead to a nearby corrugated iron shed. The journalists were escorted to that shed, where they saw ten large rockets that were about three meters long and painted olive green. The missiles were in long elongated cages, possibly used to transport them.

The soldiers said the missiles had a range of about 60 miles. A shaft in the floor led underground, but it was unclear where the shaft led and how deep it was. It seemed shallower than the first shaft.

The logo of the Qassam Brigades, Hamas's military wing, was plastered on a wall.

Later, the Israeli military published photos and videos of the shafts and other nearby facilities. A Times photographer also documented the military infrastructure.

The soldiers also took journalists to view a third tunnel shaft in a one-story farmhouse in Bureij, about a mile to the north, surrounded by farmland. They said the shaft was hidden behind a locked door, which had been blown off its hinges. Once again the journalists were not allowed into the tunnel.

Outside, about 100 yards away, military bulldozers appeared to have dug up part of the tunnel leading to the farm. Located about five meters below the surface, it was curved in shape and wide enough for one person to walk through comfortably.

Hamas has improved its ability to conceal the tunnels, but the senior official said the Israeli military had devised one of the group's operational models. The official called it the “triangle.” Whenever the Israeli army finds a school, a hospital or a mosque, the soldiers know to expect an underground tunnel system beneath them, the official said.

Destroying the tunnels is not an easy task, the official said. They must be mapped, checked for hostages and made not only damaged but beyond repair. Recent attempts to demolish the tunnels by flooding them with seawater have failed.

The official estimated it could take years to eliminate the tunnel system.

Julian E. Barnes contributed reporting from Washington.