Before Israel launched an unprecedented wave of strikes against Iran’s nuclear facilities and top military leaders this week, its spies were already on the ground in enemy territory. Israeli intelligence agency Mossad had smuggled weapons into Iran ahead of the strikes, according to Israeli security officials, and would use the weapons to target Iran’s defense from within. The officials said Israel established a base for launching explosive drones inside Iran, and the drones were later used to target missile launchers near Tehran. Precision weapons were also smuggled in and used to target surface-to-air missile systems, clearing the way for Israel’s...