As four helicopters left an undisclosed Israeli airbase in the dead of the night on September 8, the 100 elite commandos onboard braced themselves for a mission that would etch itself into the annals of Israeli military history.

Their destination was a mountain in the Ma​syaf area in western Syria,  roughly 125 miles from Israel’s northern border.

The choppers carrying the troops from the Shaldag special forces unit flew at an unusually low altitude over the Mediterranean to evade the Assad regime’s air defenses and radars as they crossed over Lebanon and into Syria.

At the same time, Israeli warplanes, navy missile ships and drones launched a major wave of strikes at the target – an Iranian missile manufacturing site cut into a large mountain.

As they landed on Syrian soil, the sounds and sparks of gunfire and explosions surrounded the troops.

They killed some 30 Syrian soldiers and guards before storming the underground facility which had been under Israeli intelligence's watchful gaze since 2017.

Codenamed “Deep Layer” by the Israel Defence Forces (IDF), the compound sits 70-130 meters underground and is almost impossible to destroy from the air.

It was a “flagship project” for Iran's efforts to arm Hezbollah on Israel’s northern border, according to the IDF, which revealed the first footage of the operation on Thursday night.

At the time, Israel had not yet invaded southern Lebanon, but was conducting airstrikes against Hezbollah as well as Iranian targets in Syria.