Shortly before attackers from Gaza poured into Israel at dawn on Saturday, Israeli intelligence detected a surge in activity on some of the Gazan militant networks it monitors. Realizing something unusual was happening, they sent an alert to the Israeli soldiers guarding the Gazan border, according to two senior Israeli security officials.

But the warning wasn’t acted upon, either because the soldiers didn’t get it or the soldiers didn’t read it.

Shortly afterward, Hamas, the group that controls Gaza, sent drones to disable some of the Israeli military’s cellular communications stations and surveillance towers along the border, preventing the duty officers from monitoring the area remotely with video cameras. The drones also destroyed remote-controlled machine guns that Israel had installed on its border fortifications, removing a key means of combating a ground attack.

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That made it easier for Hamas assailants to approach and blow up parts of the border fence and bulldoze it in several places with surprising ease, allowing thousands of Palestinians to walk through the gaps.

These operational failures and weaknesses were among a wide array of logistical and intelligence lapses by the Israeli security services that paved the way for the Gazan incursion into southern Israel, according to four senior Israeli security officials who spoke on the condition of anonymity in order to discuss a sensitive matter and their early assessment of what went wrong.

The brazen infiltration of more than 20 Israeli towns and army bases in that raid was the worst breach of Israel’s defenses in 50 years and shattered the nation’s sense of security. For hours, the strongest military in the Middle East was rendered powerless to fight back against a far weaker enemy, leaving villages defenseless for most of the day against squads of attackers who killed more than 1,000 Israelis, including soldiers in their underwear; abducted at least 150 people; overran at least four military camps; and spread out across more than 30 square miles of Israeli territory.

The four officials said the success of the attack, based on their early assessment, was rooted in a slew of security failures by Israel’s intelligence community and military, including:

— Failure by intelligence officers to monitor key communication channels used by Palestinian attackers;

— Overreliance on border surveillance equipment that was easily shut down by attackers, allowing them to raid military bases and slay soldiers in their beds;

— Clustering of commanders in a single border base that was overrun in the opening phase of the incursion, preventing communication with the rest of the armed forces;

— And a willingness to accept at face value assertions by Gazan military leaders, made on private channels that the Palestinians knew were being monitored by Israel, that they were not preparing for battle.

“We spend billions and billions on gathering intelligence on Hamas,” said Yoel Guzansky, a former senior official at Israel’s National Security Council. “Then, in a second,” he added, “everything collapsed like dominoes.”

The first failure took root months before the attack, as Israeli security chiefs made incorrect assumptions about the extent of the threat that Hamas posed to Israel from Gaza.

Hamas stayed out of two fights in the past year, allowing Palestinian Islamic Jihad, a smaller armed group in Gaza, to take on Israel alone. Last month, Hamas leadership also ended a period of rioting along the border, in an agreement brokered by Qatar, giving the impression that it was not looking for an escalation.

“Hamas is very, very restrained and understands the implications of further defiance,” Tzachi Hanegbi, Israel’s national security adviser, said in a radio interview six days before the assault.

When Israeli intelligence officials briefed senior security chiefs last week about the most urgent threats to the country’s defenses, they focused on the dangers posed by Lebanese militants along Israel’s northern border.

The challenge posed by Hamas was barely mentioned.

Hamas is deterred, the briefers said, according to one of the security officials.

In calls, Hamas operatives, who talked to one another when tapped by Israeli intelligence agents, also gave the sense that they sought to avoid another war with Israel so soon after a damaging two-week conflict in May 2021, according to two of the Israeli officials. Israeli intelligence, they said, is now looking into whether those calls were real or staged.

The next failure was operational.

Two of the officials said that the Israeli border surveillance system was almost entirely reliant on cameras, sensors and machine guns that are operated remotely.

Israeli commanders had grown overly confident in the system’s impregnability. They thought that the combination of remote surveillance and arms, barriers above ground and a subterranean wall to block Hamas from digging tunnels into Israel made mass infiltration unlikely, reducing the need for significant numbers of soldiers to be physically stationed along the border line itself.

With the system in place, the military started reducing the number of troops there, moving them to other areas of concern, including the West Bank, according to Israel Ziv, a retired major general who commanded ground forces in the south for many years, served as the head of the Israel Defense Forces’ Operations Division from 2003-05, and was recently recruited into the reserves again because of the war.

“The thinning of the forces seemed reasonable because of the construction of the fence and the aura they created around it, as if it were invincible, that nothing would be able to pass it,” he said.

But the remote-control system had a vulnerability: It could also be destroyed remotely.

Hamas took advantage of that weakness by sending aerial drones to attack the cellular towers that transmitted signals to and from the surveillance system, according to the officials and also drone footage circulated by Hamas on Saturday and analyzed by The New York Times.

Without cellular signals, the system was useless. Soldiers stationed in control rooms behind the front lines did not receive alarms that the fence separating Gaza and Israel had been breached, and could not watch video showing them where the Hamas attackers were bulldozing the barricades. In addition, the barrier turned out to be easier to break through than Israeli officials had expected.

That allowed more than 1,500 Gazan fighters to surge through nearly 30 points along the border, some of them in hang-gliders that flew over the top of the barricades, and reach at least four Israeli military bases without being intercepted.

Photos shared by one of the Israeli officials showed that scores of Israeli soldiers were then shot as they slept in their dorms. Some were still wearing their underclothes.

The second operational failure was the clustering of leaders from the army’s Gaza division in a single location along the border. Once the base was overrun, most of the senior officers were killed, injured or taken hostage, according to two of the Israeli officials.

That situation, combined with the communication problems caused by the drone strikes, prevented a coordinated response. This kept anyone along the border from grasping the full breadth of the assault, including the commanders who rushed from elsewhere in Israel to launch a counterattack.

“Understanding what the picture was of the different terrorist attacks was very difficult,” said Brig. Gen. Dan Goldfuss, an Israeli commander who helped lead the counterattack.

At one point on the ground, the general encountered — by chance — a commander from another brigade. There and then, the two men decided on an ad hoc basis which villages their respective units would try to retake.

“We decided just between ourselves,” the general said. “And that’s how we went by, from one village to another.”

All of this meant it was hard, especially in the early stages, to communicate the gravity of the situation to the military high command in Tel Aviv.

As a result, no one there sensed the immediate need for a massive, rapid air cover, even as social media emerged with reports of attacks in many communities. It took hours for the air force to arrive over much of the area, even though it has bases just minutes away in flying time, according to two of the Israeli officials and survivors of the attacks.

The fallout has been catastrophic for Israel’s security, as well as potentially damaging to its reputation in the region as a reliable military partner.

Before Saturday, “Israel was an asset to many countries in the region on security issues,” Guzansky said. “The image now is that Israel is not an asset.”

The Israeli security services do not dispute the scale of their initial failure. But they say that it can be investigated only after the war ends.

“We’ll finish this,” said Lt. Col. Richard Hecht, a military spokesperson, as the army attempted to regain control of the communities Saturday.

But, he said, “You know that this will be investigated.”

/The New York Times