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. Realising 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 afterwards, 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.

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 defences in 50 years and shattered the nation’s sense of security. For hours, the strongest military in West Asia was rendered powerless to fight back against a far weaker enemy, leaving villages defenceless 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 48km 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;