While preparing to head out to synagogue to join the dancing and celebration for the Simchat Torah festival, the rocket sirens started sounding. As we grabbed the kids and ran to our safe room (all new Israeli houses are built with one), I assumed there must have been some incident overnight, some Israeli escalation to trigger this rare but not unprecedented rocket fire on Jerusalem.

I was wrong. In a mass surprise attack, Hamas launched a huge barrage of rockets from Gaza at southern and central Israel. But this bombardment was only cover for the real attack: hundreds of armed Hamas terrorists, organised in military fashion, on technical vehicles, poured out of the Gaza strip and headed towards defenceless Israeli towns and villages nearby.

They came to kill and to kidnap, and they succeeded. Some 300 Israelis have reportedly been killed over the course of the day, and that number may rise further. Families were massacred in their homes, and terrorists seized control of several Israeli villages. Mini sieges with hostages are still ongoing tonight.

More heartbreaking, though, are the missing and the taken. Videos circulating online show terrorists bundling men, women, the elderly and young children into trucks and driving them into Gaza. Some of the victims were later paraded in the streets before being hidden in the deep tunnels underneath the strip. Israelis still don’t know if their husbands, wives or kids were killed or taken.

The country is in shock after the bloodiest day in at least 50 years. Commentators are calling it Israel’s September 11 or Pearl Harbour. But perhaps the most apt comparison is with the Yom Kippur War that began almost exactly 50 years ago: a surprise attack on a Jewish festival, a massive intelligence failure that will have far reaching consequences.

The unpreparedness of the military and security services has shocked Israelis. There was no advance knowledge, no forces on standby. It took hours for Israel Defence Forces (IDF) troops to show up at villages and towns where Hamas had time to operate freely, killing and capturing at will. Israel has always felt protected by its strong, sophisticated military. That sense of security was stripped away.

Why now? The multiple ‘rounds’ of conflict between Israel and Hamas over the last decade have mostly happened by accident after a series of escalations on both sides. Yesterday’s invasion into Israeli territory was something completely new, planned and initiated by Hamas with no direct trigger. American officials briefed a theory that Hamas was spooked by progress towards a much-hyped Israel-Saudi peace deal.

The unpreparedness of the military and security services has shocked Israelis. There was no advance knowledge, no forces on standby.

Another theory points to Israel’s internal weaknesses. After months of protests opposing the government’s plans to weaken the judiciary, Israeli society seemed more divided than ever on the eve of this new war. Military reservists had refused to serve a government they believed was abandoning democratic checks and balances, while Netanyahu’s coalition was due to advance another divisive law in the next couple of weeks, giving ultra-Orthodox Jews complete exemption from compulsory military service. Hamas perhaps saw an opportunity to attack an already-wounded polity.

In 2011, Israel exchanged one captive – IDF soldier Gilad Shalit, who was taken on active duty – for more than a thousand Palestinian prisoners. Hamas have held Avera Mengistu, a mentally ill Ethiopian-Israeli man who crossed into Gaza, for nine years. The security ransom for dozens of civilians will surely be so impossibly high that Israel cannot and will not pay it.

That only leaves rescue. Unlike the West Bank, Israeli forces haven’t operated freely in the cities of the Gaza strip since the early 1990s. Hamas had fortified every inch of these towns, made them deathtraps with deep, reinforced tunnels connecting underground bases with secret entrances into all sorts of civilian buildings.

Hamas’ surprise attack isn’t just ‘another round ’ like we’ve seen over and over since 2006: rockets on Israel, warplanes on Gaza City, dozens killed and a ceasefire after two weeks that returns things to the status quo ante. Israelis will no longer accept a return to a world where Hamas can carry out mass murder on this scale, and the country’s right-wing government is politically incapable of compromise. This war will be different. We’re all just waiting to find out how.