Iran has been seeking to strengthen air defenses because of the possibility of a military strike on Israel or the U.S. against Tehran's nuclear infrastructure, which would strike if negotiated on its enrichment plan.

Many of Iran's most advanced surface upward missiles and radars, including its long-standing Russian-made S-300 system, were destroyed or damaged by Israeli air strikes in October and April 2024.

This combined with Israel's successful strikes against Iranian agents such as Hezbollah and Yemen's Houthi rebels, which made it believed that Iran was most vulnerable to air attacks in decades.

However, many elements of Iran's defenses remain intact or appear to have been repaired in recent months, experts say.

Western intelligence assessments and satellite images reviewed by defense analysts show that Iran has since relocated several surface-to-air missile launchers, including the S-300 system, near key nuclear sites such as Natanz and Fordow.

In recent months, some kits have also been shown in public, with weapons parades in Tehran last month (including S-300 launchers and a radar truck).

According to the February military exercise, an S-300 unit was launched using Iran's new design radar, which fired a surface-up missile during the military exercise - possibly because its original radar could not operate.

"Iran certainly wants to deny the narrative that its advanced air defense measures were destroyed," she said.

Iranian Armed Forces Chief of Staff Mohammad Bagheri touted Iran's preparations for the attack this month.

"We have witnessed a significant improvement in the country's air defense capabilities and readiness," he said.

"The enemy of the Iranian nation must understand that any violation of our country's airspace will cause great damage to them," he said.

While negotiations with Washington about the future of Iran's nuclear program are underway, U.S. President Donald Trump abandoned an earlier nuclear deal with Iran during his first term, threatening to attack the Islamic Republic if negotiations break down.

Washington asked Iran to stop enriching uranium, it said it was necessary to prevent the country from obtaining nuclear weapons, while Tehran insisted it must be able to continue to enrich the use of civilians.

In April, the United States ordered six B-2 bombers (the largest aircraft deployment ever) to order from Diego Garcia, the Indian Ocean base's Diego Garcia, which is expected to be a possible launch site for any strike against Iran.

Israel has shown that it could hit Iran's air defense, which has been prompting the U.S. to support a strike against Iran. Experts say if Trump agrees to a weak deal, then Israel has a risk of attack without Washington’s consent.

During last year's strike, Israel fired targets from radar and missile sites, with its ballistic missiles fired from the S-300's highest range exceeding 200 kilometers. The missiles were built by the Israeli Rafael Corporation, which were found hundreds of kilometers in the Iraqi desert.

The effectiveness of these attacks remains controversial.

Open source satellite imagery shows some direct hits, such as on an S-300 radar truck at an aerial base near Isfahan after a strike in April 2024. However, images after the October strike show many of the S-300 sites empty, so it is unclear whether the missile has been destroyed or simply moved.

"There is not much evidence," said Sam Lair, a research assistant at the James Martin Center for Non-Diffusion Research.

However, Iran is obviously injured. Western intelligence evaluated Tehran's view of air defense capabilities last year "underperforming" and adopted measures such as repositioning and diversified launchers and radars.

Lair and the two co-authors published this month an analysis of the abstracts in the Iranian propaganda video that inadvertently reveals the interior of the air defense command center. Detailed analysis by Lair and a colleague showed that the defenses were “scattered in nature.”

But the attack on the Iranian nuclear site in a hardened underground bunker in the Natanz building will be much more complicated than anything Israel tried last year.

According to a study released in March by Royal United Services Academy in London, if the United States is involved, the Diego Garcia-based B-2 bomber could directly reduce the GBU-57 Bunker Buster bomb by 30,000 pounds.

If action is taken alone, there will be more limited options for Israel (the lack of heavy bombers or the way to deliver such large ordnance).

Rusi said they might use an F-35 stealth fighter, equipped with a 2,000-pound BLU-109 precision bomb, or an F-15 fighter bomber carrying a 4,000-pound GBU-28 bomb, both of which require slamming the same crater through a hard shelter on the same crater.

This may require many forms, and the use of medium refueling tankers itself may be vulnerable to long-range ground-up missiles or drones. Israel has targeted at least nine times in Yemen since last summer, similar to Iran's strike.

They will also be well listed in action arrays of short and medium ground missiles, as well as wandering air defense drones, which Iran has placed on air defense. It is difficult to know how many of them were destroyed before a consistent bombing campaign began.

In addition to short-range systems like the Russian Tor-M1, Iran's Arsenal also includes locally developed surface-to-air missiles such as the long-range Bavar-373 and the medium-sized Khordad-15. Fabian Hinz, a researcher at the UK-based Institute for International Strategic Research, said the indigenous weapons plans were frustrated by Russia's slow delivery and refused to sell more advanced systems, such as the S-400.

"From the Iranian side, this effort attempts to replicate the success story of Iran's ballistic missile development plan," he said.

Jon Alterman, president of Global Security and Inter-Earth, a Washington-based Center for Strategic and International Studies, said such defense capabilities against Israel are not direct. "But is it beyond Israel's capabilities? No, of course not. Israel has been training for this situation for decades."

The same is true for Iran. Before bombing the nuclear site, Iran's air defense measures will be one hour or even a few days of combat, using weapons and cruise missiles to confront electronically disturbed aircraft and anti-radiation missile-backed fighters and cruise missiles to destroy radar.

“Israel has established Iran’s air dominance,” said Robert Tolllast, a researcher at British think tank Russi. "But such a strike will require a wave of aircraft and a wave of aircraft within a few hours. Crew fatigue enters the picture. The longer Iran is, the greater the chance of a problem."

He said Iranian radars are vulnerable to radiation-seeking missiles and have to shut down their survival, which may be blinded by Israeli obstacles. But even if most of Iran's high-end air defenses are subdued or destroyed, there are some systems that can be lucky.

“You have a very fierce air battle and there is a good chance that you will be marching Israeli pilots on Iranian TV.”

Even Iran's high-level missiles could succeed. Syria, for example, knocked down the Israeli F-16 in 2018 and used the S-200's surface toward air missiles, a Russian system that began in use in the late 1960s. The plane crashed in northern Israel and both pilots survived.

Yuri Lyamin, an air defense expert and top expert in Russian air defense systems at the Moscow Center for Strategic and Technical Analysis, said the success of the attack would not be scheduled.

"While everyone pays attention to the S-300, Iran places great importance on creating the most mobile, modern air defense systems that can quickly change locations and hide in shelters, making it less susceptible to strikes by long-range missiles," he said.

The result “depending on the joint efforts of the attackers, and the ability of the defensive forces to work together. The best team will win”.

Other reports by Bita Ghaffari in Tehran