The U.S. closely monitored Israel's military bases and eavesdropped on secret communications in 2012, fearing its longtime ally might try to carry out a strike on Fordow, Iran's most heavily fortified nuclear facility. Nerves frayed at the White House after senior officials learned Israeli aircraft had flown in and out of Iran in what some believed was a dry run for a commando raid on the site. Worried that Israel might ignite a regional war, the White House sent a second aircraft carrier to the region and readied attack aircraft, a senior U.S. official said, in case all hell broke loose." The two countries, nursing a mutual distrust, each had something to hide. Instead of talking to each other, the allies kept their intentions secret. To figure out what they weren't being told, they turned to their spy agencies to fill gaps. They employed deception, not only against Iran, but against each other. After working in concert for nearly a decade to keep Iran from an atomic bomb, the U.S. and Israel split over the best means: diplomacy, covert action or military strikes. In 2010, the risk of covert action became clear. A computer virus dubbed Stuxnet, deployed jointly by the U.S. and Israel to destroy Iranian centrifuges ... had inadvertently spread across the Internet. The Israelis wanted to launch cyberattacks against a range of Iranian institutions, according to U.S. officials. But the breach made Mr. Obama more cautious, officials said, for fear of triggering Iranian retaliation, or damaging the global economy if a virus spread uncontrollably.