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By Jeremy Bowen
International editor, in southern Israel
On the car radio the main news channel was full of the new reality, with freshly recorded stings for the hourly bulletins.
"Israel at War" boomed a bass voice, punctuating reports of continued fighting between the Israeli military and Hamas infiltrators, and air raid alarms close to the border with Lebanon. On the other side of the fence is Hezbollah, the powerful Iranian-backed Lebanese militia that is Israel's most formidable enemy.
The prospect that it might enter a two-front war is Israel's strategic nightmare.
Outside a military base on the highway that goes south to Gaza hundreds of cars were parked along both hard shoulders and on the central reservation. They were left by reservists who had reported for duty. More were arriving.
A man standing next to the open tailgate of his hatchback pulled on a crumpled olive-green army shirt. He fished around inside the back to find his body armour, slammed the door, and went to join the rest of his reserve unit.
A middle-aged couple had managed to meet up with their son, a young man of around 20 who is doing his compulsory military service. The mother handed over a jar of home-made pickles.
The father said: "We've told him to concentrate on what he has to do, and not to think too hard about friends who've been hurt and killed."
More armed men have entered Israel through breaches in the wire that was designed by Israel to contain Hamas.
Israelis are incredulous that their army is taking so long to regain control of the land and villages bordering Gaza. One unit appealed on social media for drones, others have asked for sleeping bags and food.
Israel's military is powerful, well capable of driving Hamas back. But its failure to do so thus far is reinforcing the conviction that the country's lavishly-funded and prestigious military and intelligence establishment should have stopped a catastrophe and did not.
Constant comparisons are being made between the events of the last few days and the war exactly 50 years ago, that started in October 1973 after a surprise attack by Egypt and Syria.
Golda Meir, the prime minister at the time, ignored warnings that an attack was coming on a Jewish holiday, and was condemned for hubris and complacency.
The same accusations are already being thrown at her successor Benjamin Netanyahu, by his many political enemies.
Israel is still bitterly divided about Mr Netanyahu, whose government's extreme right-wing agenda prompted months of protests.
But citizens of all political persuasion are rallying behind their flag. With Israel officially at war the protests are suspended, and reservists who refused to turn up for duty are now queuing to return.
Israelis, collectively, are reeling from the shock of the Hamas attack.
As survivors and victims tell their stories, the desire deepens to punish Hamas for the way its men went from house-to-house killing families and children in Israeli border communities. As we drive, callers phoning in to the radio are talking about parents who had calls from their terrified children at the rave in the desert where Hamas massacred hundreds of civilians.
They're haunted that parents heard the shots that killed their sons and daughters.
"Israel at War", the sting comes again, with a report from the Israeli minister of defence Yoav Gallant, a former general, speaking somewhere in southern Israel. "We're fighting animals," he says, "and we'll act accordingly." Food, water and power supplies to Gaza are being cut.
My phone pings. A post on the BBC Jerusalem office WhatsApp group says that a market in Gaza has been hit and many killed as Israel attacked what it said was a Hamas target. The video of broken bodies feels like a harbinger of something even worse.
The scale of the bloodshed inflicted on Israel by Hamas is unprecedented. An organisation that planned its attack so carefully will have been aware that Israel's response would be ferocious.
Israel's war plans will be complicated by the presence of around 100 hostages taken in the attack. But one cabinet minister, according to a cabinet leak reported in the Israeli press, has said that should not hold them back.
This feels very different to the regular confrontations Israel and Hamas have had since the militant group took over Gaza in 2007. They were serious enough.
Over the years Israel caused immense damage and inflicted thousands of casualties on Palestinian civilians. But they had fallen into a familiar pattern and felt at times like deadly rituals.
Now both sides are in unknown territory.