The commandos came in helicopters, on a nearly moonless night.

The guards outside the secret weapons lab in northwestern Syria had already been killed in a short series of airstrikes when the thrumming of Israeli Air Force helicopters approached.

At first the Sept. 8 strike seemed like many others carried out by Israel, which had long had the facility in its sights. Israeli officials believed that Iran and the Lebanese militia Hezbollah planned to manufacture a new generation of precision missiles there.

But this was a different kind of operation. The helicopters flew low, without lights. Soon dozens of camouflage-clad commandos were rappelling down cables and rushing into the complex, which in places was more than 200 feet underground, according to U.S., European and Israeli officials.

What followed was one of the most daring Israeli military operations against Hezbollah in years.

In the panoply of Israeli strikes and assassinations since the deadly Hamas-led attack on Oct. 7, the commando raid stands out. Israel sent special operations troops, boots on the ground, into a sovereign country to carry out a mission.

It initially looked to be a one-off attack on a Hezbollah weapons facility, but it now appears to have been the opening salvo in a covert-in-name-only campaign against the Iranian proxy group.

Hezbollah began attacking northern Israel soon after Oct. 7, and the two sides have been exchanging fire ever since. Then on Sept. 17, about a week after the raid, thousands of pagers carried by Hezbollah members exploded across Lebanon. The next day, hundreds of walkie-talkies used by the militants detonated. Israel has neither confirmed nor denied a role in the attacks, which killed dozens of people and injured more than 3,000.