Iran’s attack on Israel: What happened and why

The slow-moving, telegraphed attack drew a robust military defense from Israel, the U.S. and other allies and resulted in minimal damage on the ground. But it was a game-changer.

Here is a summary of what led to the Iranian attack, what transpired and what to expect next.

Airstrike in Syria lights the fuse

Iran planned its attack on Saturday as a response to an April 1 airstrike in Damascus, Syria, that hit what Tehran said was a diplomatic building, killing seven members of Iran’s Islamic Revolutionary Guard Corps and some staff. At the top of the list of those killed was Gen. Mohammad Reza Zahedi, a senior commander who managed Iranian paramilitary operations in Lebanon and Syria.

Israel has conducted hundreds of airstrikes against Iranian targets and Tehran’s militia allies in the Middle East in its yearslong effort to degrade the military power of Iran, which Israel views as a threat to its existence as a nation. Israel didn’t confirm or deny responsibility for the Damascus attack, and said that the building was used by Iran’s Quds Force and disguised as a civilian site.

Iran said the building had diplomatic status and that the strike was akin to an attack on Iranian territory. That interpretation, and the seniority of the military officials who were killed, signaled that the rules of engagement had changed in what had been a covert military conflict.

Iran vows to respond

The day after the airstrike in Damascus, Iran’s Supreme Leader Ayatollah Ali Khamenei and President Ebrahim Raisi publicly threatened to retaliate against Israel. The pledge by the leadership in Tehran put Iran on course for a direct attack.

As of this point, Iran had avoided direct confrontation, instead arming and employing militia allies in countries around the Middle East, such as Hezbollah in Lebanon and the Houthis in Yemen, to target Israel and U.S. interests in the region.

U.S. sounds the alarm and mobilizes forces

By Wednesday, April 10, U.S. officials said that intelligence reports indicated an attack on Israeli assets by Iran or its militia allies could be imminent. That day, President Biden warned that Iran was “threatening to launch a significant attack on Israel."

In the days that followed, the U.S., expecting a weekend attack, repositioned warships to protect Israel and American forces in the Middle East. “We will support Israel and help defend Israel and Iran will not succeed," Biden said.

Iran launches drones and missiles toward Israel

At around 11 p.m. local time Saturday in Israel, Iran declared that it was launching a swarm of drones and missiles toward Israel. Around the same time, Israel’s military said more than 100 drones were headed toward the country.

Prime Minister Benjamin Netanyahu quickly convened Israel’s war cabinet—a group formed for the war with Hamas in Gaza. The Israeli military declared the Iranian attack to be “a severe and dangerous escalation."

Iran and Israel are more than 1,000 miles apart—giving Israel around nine hours to prepare for the arrival of the drones or intercept them en route.

Shortly after the Iranian announcement, Israel’s military confirmed that Iranian missiles were also on the way. Iran’s cruise missiles, according to military analysts, would take around two hours to reach Israeli territory. Its high-speed ballistic missiles would take around 12 to 15 minutes.

Air-raid sirens sounded across Israel, and explosions were heard over Jerusalem as Israel’s air defenses kicked in. In some areas, people were directed to remain in bomb shelters.

Meanwhile, roughly two hours after the launch, Iranian officials declared that Iran had concluded its retaliation for the attack in Damascus—while warning the U.S. to stay out of the fight. At this point, the U.S. and Israel were fully engaged in defending the country.

A multinational defense

Around an hour after Iran launched its drones, the U.S. was already reporting success in downing them. In the end, most of the Iranian drones and the missiles that launched successfully were destroyed before they reached Israeli airspace.

The successful defense of Israel was a combination of Israel’s sophisticated air-defense system and assistance provided by the U.S. and other Western and Arab partners. Israeli, American, British and Jordanian warplanes played a role.

A small number of missiles landed in Israel, causing light damage to a military base in the south. A hospital said it was treating 12 people after the attacks.

In all, Iran launched more than 170 drones, around 120 ballistic missiles and about 30 cruise missiles, according to Israel. The use of ballistic missiles represented an Iranian show of strength—and shortcomings: Roughly 50% of these missiles failed to launch or crashed during flight before reaching their target, U.S. officials said.

Iran had ensured that its salvo came as no surprise, giving some Arab countries advance notice, including details on the timing, according to Arab officials. Iran’s foreign minister said Sunday that the country had warned its neighbors 72 hours before it began the attack.

Israel’s next move

As Israelis returned to the streets on the morning after, a debate began. A decisive strike on Iran—some Israeli politicians called for a “crushing" attack—would raise the stakes yet again, but a weak response could erode Israeli deterrence. Israel’s war cabinet convened but didn’t say how it would respond. Iranian officials warned of a much stronger response if Israel retaliates.

In the U.S., Biden pressed for a diplomatic solution. If Israel does decide on a military response, whatever it may be, Biden and administration officials declared that the U.S. wouldn’t be a part of it.

Dov Lieber, Anat Peled, Gordon Lubold, Laurence Norman and Yaroslav Trofimov contributed to this article.

Write to Peter Saidel at Peter.Saidel@WSJ.com