When a swarm of drones and cruise missiles attacked Saudi Arabia’s biggest oil facility on Sept. 14, an outraged Trump administration quickly blamed Iran for what it called an “unprecedented attack” on global energy supplies. But the real surprise was the strike’s accuracy: Of 19 weapons used, all but two scored direct hits.

When the smoke cleared, Saudi officials counted 14 holes where incoming projectiles had sliced through petroleum storage tanks. Three other critical parts of the oil-processing facility had been hit and disabled, shutting down the facility and temporarily cutting Saudi oil production in half.

In subsequent reports, U.S. analysts would describe the attack as a kind of wake-up call: evidence of a vastly improved arsenal of high-precision missiles that Iran has quietly developed and shared with allies over the past decade. In the event of a wider war with the United States, Iran would probably deploy such weapons to inflict substantial damage on any number of targets, from U.S. military bases to oil facilities to sites in Israel, analysts say....

Because Iran has provided its advanced missiles and bombmaking technology to proxy groups, it also possesses options for harming its adversaries while limiting the risk of reprisals. In the past, Tehran frequently tasked pro-Iranian militant groups — chiefly the Lebanon-based Hezbollah, but also proxies and sympathizers based in Syria, Iraq, Yemen and Bahrain — with carrying out a wide range of covert actions on its behalf, from bombings and missile strikes to kidnappings and cyberwarfare....