When Israeli fighter jets roared off the runways on Friday night, on a thousand-mile run to Iran, they headed for two major sets of targets: the air defenses that protect Tehran, including Iran’s leadership, and the giant fuel mixers that make propellant for Iran’s missile fleet.

Israel’s military leaders, in calls with Defense Secretary Lloyd J. Austin III and other senior American officials, had concluded that taking out the air defenses would make Iran’s leaders fearful that Tehran itself could not be defended. That feeling of vulnerability was already high, after Israel decimated the leadership of Hamas and Hezbollah, Tehran’s proxy forces that could strike Israel, over the past month.

The surprise element for the Iranians was a set of strikes that hit a dozen or so fuel mixers, and took out the air defenses that protected several critical oil and petrochemical refineries, according to a senior U.S. official and two Israeli defense officials who spoke on condition of anonymity to discuss internal planning.

Without the capability to mix fuel, Iran cannot produce more of the type of ballistic missiles that its forces fired on Israel on Oct. 1, the immediate provocation for Israel’s strike. And it could take more than a year to replace them from Chinese and other suppliers.

By Saturday, American and Israeli officials were claiming a major success, but lurking behind the satisfaction with the tactical gains lies a longer-term worry. With Iran’s Russian-produced air defenses in smoldering piles, many fear the Iranian leaders may conclude they have only one defense left: racing for an atomic weapon.

That is just what American strategists have been desperately trying to avoid for a quarter-century, using sabotage, cyberattacks and diplomacy to keep Tehran from crossing the threshold to become a full nuclear-armed power.