A senior Israeli official, speaking on condition of anonymity, said the military has so far discovered far more tunnels — 40 and counting — than Israel had previously thought existed. The number came as a surprise, as did the sophistication of the tunnel network. Current and former officials said that Israeli intelligence and political leaders knew that the tunnels were fortified with concrete and had space to store weapons and food. But Israeli intelligence analysts and political leaders didn’t comprehend that the tunnels were wide enough to move several Hamas fighters into the country at a time, and they didn’t realize how many of the tunnels ended up in Israel, particularly near civilians. (A Hamas video that shows fighters emerging from a tunnel and attacking an Israeli military installation provides a vivid example of why Israelis have so come to fear the clandestine attacks.)

“Of course we didn’t know all the details and how complex was the network below the ground. I don’t think we had the full picture,” said Giora Eiland, a retired major general in the Israel Defense Forces (IDF) who served as Israel’s national security advisor from 2004 to 2006. “But I would emphasize that we did not fully understand the operational consequences of the use of tunnels by [Hamas].”

Eiland said that Israeli intelligence knew the locations of some tunnels, but that analysts didn’t understand some key details such as the strength of the concrete used to build the tunnels.