For much of the last decade, as Iran methodically built its nuclear program, Israel has been assembling a multibillion-dollar array of high-tech weapons that would allow it to jam, blind, and deafen Tehran's defenses in the case of a pre-emptive aerial strike.

A U.S. intelligence assessment this summer, described to The Daily Beast by current and former U.S. intelligence officials, concluded that any Israeli attack on hardened nuclear sites in Iran would go far beyond airstrikes from F-15 and F-16 fighter planes and likely include electronic warfare against Iran’s electric grid, Internet, cellphone network, and emergency frequencies for firemen and police officers.

For example, Israel has developed a weapon capable of mimicking a maintenance cellphone signal that commands a cell network to “sleep,” effectively stopping transmissions, officials confirmed. The Israelis also have jammers capable of creating interference within Iran’s emergency frequencies for first responders.

In a 2007 attack on a suspected nuclear site at al-Kibar, the Syrian military got a taste of this warfare when Israeli planes “spoofed” the country’s air-defense radars, at first making it appear that no jets were in the sky and then in an instant making the radar believe the sky was filled with hundreds of planes.

Israel also likely would exploit a vulnerability that U.S. officials detected two years ago in Iran's big-city electric grids, which are not “air-gapped”—meaning they are connected to the Internet and therefore vulnerable to a Stuxnet-style cyberattack—officials say.

A highly secretive research lab attached to the U.S. joint staff and combatant commands, known as the Joint Warfare Analysis Center (JWAC), discovered the weakness in Iran’s electrical grid in 2009, according to one retired senior military intelligence officer. This source also said the Israelis have the capability to bring a denial-of-service attack to nodes of Iran’s command and control system that rely on the Internet.

Tony Decarbo, the executive officer for JWAC, declined comment for this story. The likely delivery method for the electronic elements of this attack would be an unmanned aerial vehicle the size of a jumbo jet. An earlier version of the bird was called the Heron, the latest version is known as the Eitan. According to the Israeli press, the Eitan can fly for 20 straight hours and carry a payload of one ton. Another version of the drone, however, can fly up to 45 straight hours, according to U.S. and Israeli officials.

Unmanned drones have been an integral part of U.S. wars in Iraq, Afghanistan, and Pakistan, gathering intelligence and firing missiles at suspected insurgents. But Israel's fleet has been specially fitted for electronic warfare, according to officials.

The Eitans and Herons would also likely be working with a special Israeli air force unit known as the Sky Crows, which focuses only on electronic warfare. A 2010 piece in The Jerusalem Post quoted the commander of the electronic warfare unit as saying, “Our objective is to activate our systems and to disrupt and neutralize the enemy’s systems.”

Fred Fleitz, who left his post this year as a Republican senior staffer who focused on Iran at the House Permanent Select Committee on Intelligence, said in his meetings with Israeli defense and intelligence officials, they would always say all options were on the table.

"I think Israel has the capabilities with their air force and mid-air refueling to take on these sites," said Fleitz, who is now managing editor of Lignet.com. "They would have to take out radar and anti-aircraft. They could also attack with missiles and their drone fleet."

Whatever Israel ultimately decides to do about Iran’s program, one mission for now is clear. A senior Israeli official told The Daily Beast this month that one important objective of Israel's political strategy on Iran was to persuade Iranian decision makers that a military strike against their nuclear infrastructure was a very real possibility. "The only known way to stop a nuclear program is to have smashing sanctions with a credible military threat. Libya is the best example of this," this official said.

At the same time, if past practice is any guide, the Israelis would not likely strike at the same moment that their officials are discussing the prospect in the press. In other words, if Israel is openly discussing a military strike, it is unlikely to be imminent.

But if Israel goes radio silent—like it did in when it attacked a suspected nuclear site in Iraq in 1981—that may be an early warning sign that a strike is nearing.

When Sam Lewis was U.S. ambassador to Israel during the transition from the Carter to Reagan administrations, he warned the new administration there was a chance then-Prime Minister Menachem Begin might bomb the Osirak nuclear reactor in Iraq.

“I had given a full alert to the new administration about the dangers,” Lewis recalled in an interview. “We’d been having discussions with the Israelis about how they wanted to stop the project, there was a lot of news and then it all dried up.”

Lewis and his staff had moved on. Then without warning on June 7, 1981, in something called Operation Opera, Israeli jets flew in late afternoon via Jordanian airspace and incinerated the nuclear facility that was under construction southeast of Baghdad. “I did feel after the fact that we should have assumed this bombing was going to take place,” Lewis said. “After it was over, I was not surprised, I was annoyed by having been misled by the quiet as it were.”

There may be a lesson for the Obama administration as it tries to calibrate what Israel will do on Iran. Since taking office, the president has made major efforts to avoid any surprises in the relationship with Israel, particularly on the issue of Iran. Obama and Israeli Prime Minister Benjamin Netanyahu, for example, tasked their first national security advisers to establish an unprecedented system for regular consultation between the two countries, featuring regular video-teleconferences.

They formed a standing committee on Iran as well, to check the progress of sanctions, share intelligence, and keep both sides informed. Despite all of this, Netanyahu has refused to give any assurance to Obama or his top cabinet advisers that he would inform or ask permission before launching an attack on Iran that would likely spur the Iranians to launch a terrorist attack on the United States or Israel in response, according to U.S. and Israeli officials familiar with these meetings. The Telegraph first reported the tension over the weekend.

Defense Secretary Leon Panetta "expressed the desire for consultation on any contemplated future Israeli military action, and [Ehud] Barak understood the U.S. position,” said one official familiar with the discussions.

The Israelis may be coy this time around because of the experience of then-Israeli Prime Minister Ehud Olmert. In 2007, the Israelis presented what they considered to be rock-solid evidence that Syria was building a covert nuclear facility at al-Kibar. They asked President Bush to bomb the facility, according to the new memoir from Condoleezza Rice.

“The president decided against a strike and suggested a diplomatic course to the Israeli prime minister,” she wrote. “Ehud Olmert thanked us for our input but rejected our advice, and the Israelis then expertly did the job themselves.”

One American close to the current prime minister said, “When Netanyahu came into office, the understanding was they will not make the same mistake that Olmert made and ask for something the president might say no to. Better to ask forgiveness than to ask permission.”