Paul Iddon Contributor

Israeli officials believe that a potential Iranian acquisition of advanced Russian S-400 air defense missile systems could complicate a potential strike against that country's nuclear program. But would an S-400 acquisition really give Tehran a game-changing capability given that it already possesses some formidable long-range air defense systems?

On Mar. 11, Iranian state media reported that Iran had finalized a contract for buying Su-35 Flanker-E fighters. Tehran is expected to receive at least two dozen jets built initially for Egypt.

Earlier in the month, Bloomberg reported that Iran is also seeking S-400s. It cited unnamed American and Israeli sources warning that such an acquisition would hasten any decision to launch a strike. It also said it would take less than two years for any Iranian S-400s to become operational.

However, it has yet to be seen if Russia will ultimately fulfill an Iranian request for such advanced systems.

Anton Mardasov, an independent Russian analyst and non-resident scholar of the Middle East Institute's Syria program, noted that the "new wave of rumors" concerning an Iranian S-400 contract coincides with rumors of Iran deploying advanced indigenous air defense systems in Syria.

"Of course, it cannot be ruled out that Tehran did indeed demand S-400 deliveries from Russia for its support in the war in Ukraine through deliveries of kamikaze drones (loitering munitions)," he told me. "However, it is important for Iran to develop its own military-industrial complex, supervised by the IRGC (Islamic Revolutionary Guard Corps), and this military-industrial complex produces an analogue of the Russian S-300 complexes."

Mardasov noted that the reports on the supply of S-400s and the deployment of Iranian air defense systems in Syriawith tacit Russian consent suggest a new military alliance between the two, something he notes is not the case.

Iran acquired long-range S-300 PMU-2 systems from Russia in 2016 as part of a contract signed in 2007. In recent years it has also developed indigenous high-altitude air defense systems such as the Khordad 15 and Bavar-373. It boasts that the latter has equivalent capabilities to the S-400.

Even without S-400s, any U.S. or Israeli attack on Iran's nuclear sites would have to first assess how to evade or destroy an already formidable air defense due to the rapid progress Iran has made in just a few short years.

Nevertheless, any potential S-400 procurement could further enhance and strengthen this air defense.

"In terms of capabilities compared to the S-300, the S-400 is meant to have better anti-stealth capabilities, making it a greater potential threat to the F-35 and F-22 in the Israeli and American forces," Ryan Bohl, a senior Middle East and North Africa analyst at the risk intelligence company RANE, told me.

"We have not yet seen the S-400 used against these fifth-generation fighters, so right now, these claims are on paper."

He noted that the S-400 generally outpaces the S-300 when it comes to range but also pointed out that the upgraded S-300 PMU-2s, the same variant Russia supplied Iran in 2016, can close that gap.

"The Bavar-373 is also an untested system against fifth-generation fighters, despite Iranian claims," he said. "On paper, it is meant to rival or even replace the S-400 in terms of range, targeting, and anti-stealth technology."

It remains unclear how well U.S.-built fifth-generation F-35 or F-22 stealth fighters would fare against the S-400. While Russia has had the S-400 deployed in Syria for years now, it has deliberately avoided using them to target Israeli warplanes that frequently attack suspected Iran-related targets throughout that war-ravaged country.

A picture shows two Russian S-400 Triumf S-400 Triumf missile system at the Russian Hmeimim ... [+]

AFP VIA GETTY IMAGES

"We do know that the more advanced S-300 PMU-2s have not blocked some Israeli covert action via drone inside Iran; the February Isfahan attack indicated Iran will struggle to block such strikes," Bohl said. "We also know that Russian air defenses inside Russia itself have also failed to block older Soviet-made drones used by the Ukrainians as well, which does suggest that even advanced S-400s may not be as capable as they appear on paper."

Nevertheless, a combination of S-400s and Su-35s could prove a formidable adversary for any force that attempts an attack against Iran if deployed effectively.

"In all likelihood, even if they underperform on paper, S-400s and Su-35s would, if used by well-trained crews and integrated into a professionalized air defense system, create more complications for Israeli/U.S. military campaigns against Iran," Bohl said. "At the very least, they would be advanced systems that Israeli covert action would seek to avoid, while in the case of overt military action, they would be high-value targets that would have to be neutralized for Israel and/or the U.S. to strike Iran's nuclear program successfully."

Then there is the question of how Israel might respond if Russia does deliver Iran these missiles despite its strong objectives. In response, might Israel reverse its longstanding policy against supplying Ukraine with lethal weaponry?

"It is clear that air defense supplies are not really a red line for Israel since these are really defensive weapons and they are purchased simply to have more advanced systems in service," Mardasov said. "But in a situation where Russia is somehow helping Iran to modernize its strike capability in view of its use in the Ukraine war, the supply of S-400 could upset the already fragile balance in Russia-Israel relations."

Bohl believes Israel would be more likely to send indigenous systems such as its Iron Dome or Barak-8 to help upgrade Ukraine's air defense if Russia pushes ahead with an S-400 delivery to Iran. He anticipates that such a scenario would pose a "headache" to Russian military designs in Ukraine.

"This is a notable constraint to a Russian delivery to Iran," he said. "As noted above, at the end of the day, Moscow must make a political decision to deliver to Iran and accept that will likely push Israel closer to Ukraine, even if that doesn't necessarily result in immediate delivery of advanced Israeli air defenses to Ukraine."

"It could also drive cooperation in intelligence, encourage the Israelis to be more aggressive in Syria, and/or cause Israel to deliver other equipment to Ukraine, like small arms, mortars, and anti-tank missiles."