Forget drones, its Iran's precision missiles that deter invasion

“This precision strike capability means that Iran can make a calibrated response to any US action targeting an oil facility or military site in tit-for-tat strikes which limits the idea of ‘deterrence by punishment’,” said Dr Jack Watling, a Research Fellow at RUSI. “People will think twice about fighting them, even if Tehran is left weaker than their opponents. They give Iran scope to fight by proxies knowing huge retaliation is unlikely.”