“Of course we are scared,” said Dan, a 35-year-old reservist on his way to a military base in Israel, declining to give his full name or location due to concerns for his family. “We are afraid, but we are focused.”

Some Israelis have volunteered for military service despite being out of the age range for reservists. “I lost my father, uncle and cousin in the Yom Kippur War,” Israeli entrepreneur Noam Lanir, 56, said in a phone call from Tel Aviv, where he had volunteered to fight alongside his two sons. “Now it is my time.”

Already, this is the largest mobilization in Israel since the 1973 Yom Kippur War half a century ago, when 400,000 reservists were called up after Egypt and Syria led Arab armies in a surprise attack on Israel. Authorities said that the speed of this mobilization was even greater than in that famous war.

Israel Defense Forces (IDF) spokesperson Daniel Hagari said on Monday that Israel “has never mobilized so many reservists so quickly,” with 300,000 reservists called up within 48 hours. The sheer speed of the mobilization would be impossible for most nations, experts said.

“In terms of cold start capability the IDF remains unmatched by the rest of the world,” defense analyst Franz-Stefan Gady wrote on X, formerly known as Twitter.

Military service is compulsory for all Israelis when they turn 18, though there are some exceptions. After this, they are assigned to the reserve and can be called upon to serve periodically until the age of 40.

The mobilization comes at a crisis point. Hamas launched an unprecedented attack Saturday on Israel, firing rockets and infiltrating across the border; Israel responded with airstrikes and a declaration of war. U.S. officials expect Israel to launch a ground incursion into Gaza this week.

Families have been divided by the mobilization. Speaking from Leeds, England, Tal Kasuto said that his family WhatsApp group had been wracked with anxiety and messages of love since one of his sisters was mobilized.

“It’s a scary thought,” Kasuto said of his 23-year-old sister, Adi, leaving her home in Tel Aviv and the relative safety of her day job in retail to join troops to fight a war. Adi’s twin, Ayelet, had not yet been mobilized.

“They have always had each other,” Kasuto said of his sisters. “They are so close.”

Dan, who left behind his job as a supply chain and operations consultant to fight, said that parting with his two children — one of them 3 years old and another 9 months — was “very hard.”

“I hugged and kissed my wife,” he said, before adding, “My beautiful wife.” As long as he has access to his phone, he said, he will use it to send her updates, to let her know he is okay.

He said he does not know what his exact mission will be. He said that while it was not compulsory for him to step up, he wanted to volunteer. “You have to do whatever it takes,” he said.

“I’ve never seen anything like this,” David Citron, a 32-year-old venture capitalist now working as a combat medic, said by phone from where he is stationed near Gaza, as explosions from the Iron Dome rocket interceptor system could be heard in the background.

“Thousands and thousands of soldiers, everyone just making their way onto base. A lot of anger, a lot of frustration, a lot of shock,” he added. “A lot of people were completely blindsided, myself included.”

There have been some signs of chaos in the reservist process, with some Israelis complaining of uncertainty about their role. In WhatsApp groups used by Israelis abroad, some have also complained of sharp price increases in tickets for flights back home.

At the check-in queue for an Israir Airlines flight from Berlin to Tel Aviv on Monday, a few dozen Israelis waited in the hopes of getting on a flight home. Check-in staff announced that priority would be given to those answering Israel’s unprecedented call-up of reservists.

“Military first,” said one, as he indicated that he could only take 10 people from the ticketless line.

With a slew of carriers canceling flights to Tel Aviv as rockets target the airport, Israelis mobilized while abroad have limited options to get home. El Al, the national carrier, has announced that it will schedule extra flights to help people get home. Two Hercules transport planes have also been flown to European countries to bring home Israelis, according to the IDF.

Israeli reservists returning to the country at Miami International Airport, which has a direct El Al flight to Tel Aviv, told local news reporters that flights were full. “People are connecting. They want to pray. They want to unite,” Rabbi Levi Kurinsky, who serves at the Chabad of the airport, told Local 10 news.

The Israeli Embassy in Peru has helped arrange a flight to Tel Aviv from Lima, given the large number of Israelis who had been traveling in South America at the time of the attack.

“It was probably the best flight I was ever on in the worst possible circumstances,” said Yehuda Brownstein, a 24-year-old Israeli American living in Los Angeles, who had not been called up for reserve duty but bought the first ticket he could find to Tel Aviv after hearing the news on Saturday anyway.

The emotions on the flight were mixed, he said. At one point before they landed, everyone on the plane stood up and sang the national anthem in memory of those who had died. “There really was this connectedness between everyone in that cabin on that flight — everyone there for the same cause,” he said.

The conflict has bridged some divides in Israel. Lanir, the entrepreneur, is also one of the leaders of Brothers and Sisters in Arms, a group of reservists who have been protesting the Israeli government’s plan to limit the Supreme Court’s power.

Now, he is using his private jet to fly people into Israel from Italy and Greece. Those on board his plane are seeking information about their loved ones, many of them dead or missing. Lanir said Israeli officials have been granting him permission to operate the flights on a humanitarian basis.

“I’m sending my private jet to whoever needs it,” he said. “We survived Auschwitz, we survived the Yom Kippur War. We will survive this.”

Hassan reported from London and Taylor from Washington. Loveday Morris in Berlin, Bryan Pietsch in Washington and Gerrit De Vynck in San Francisco also contributed to this report.