A Russian S-400 missile system rolls down the street during a parade rehearsal May 6, 2018, in Moscow. Military analysts assess Russia’s S-400 as being capable of detecting and destroying stealth fighter jets flown by Israel and the United States.

A Russian S-400 missile system rolls down the street during a parade rehearsal May 6, 2018, in Moscow. Military analysts assess Russia’s S-400 as being capable of detecting and destroying stealth fighter jets flown by Israel and the United States. (Wikimedia Commons)

Last March, a Russian arms maker invited a delegation of Iranians to a VIP shopping tour of its weapons factories. The 17 visitors were treated to lunches and cultural shows and, on the final day, toured a plant that makes products long coveted by Tehran: advanced Russian air-defense systems for shooting down enemy planes.

The factory, NPP Start, in the city of Yekaterinburg, is under U.S. sanctions for supporting Russia’s war against Ukraine. Among its wares are mobile launchers and other components for antiaircraft batteries - including Russia’s S-400, which military analysts assess to be capable of detecting and destroying stealth fighter jets flown by Israel and the United States.

A leaked Russian document, part of stolen Iranian emails posted online in February by a hacker group, described the tour as a showcase for “scientific and technical potential and production capabilities” that Russia could offer Iran.

Whether the visit led directly to a purchase is unknown. But the trip is emblematic of what intelligence officials describe as a deepening strategic partnership between Moscow and Tehran in the two years since Russia’s full invasion of Ukraine - an alliance that could emerge as a significant factor as Israeli leaders weigh possible military strikes in retaliation for the hundreds of drones and missiles launched against Israel over the weekend.

Iran opened a dangerous new chapter in its relations with Russia by agreeing in 2022 to supply thousands of battlefield drones and missiles to aid Moscow in its war against Ukraine. The expanded ties have now helped cement agreements between Moscow and Tehran, including a pledge by Russia to provide its ally with advanced fighter jets and air-defense technology, assets that could help Tehran harden its defenses against any future airstrike by Israel or the United States, according to U.S., European and Middle Eastern intelligence officials and weapons experts. The officials, like several others interviewed for this article, spoke on the condition of anonymity to discuss sensitive matters.

It is not known how many of the systems have been provided and deployed, but Russian technology could turn Iran into a far more formidable adversary, with an enhanced ability to shoot down planes and missiles, the officials and experts said.

The weapons deals, some details of which have not been reported previously, are part of a broader collaboration that includes co-production of military drones inside Russia, the sharing of anti-jamming technology and real-time battlefield assessments of weapons deployed against NATO-equipped forces in Ukraine, the intelligence officials and weapons experts said. The cooperation is reaping substantial benefits for both countries, while elevating Iran’s status from junior ally to strategic partner, they said.

“It’s no longer the patron-client dynamic, where Russia holds all the leverage,” said Hanna Notte, director of the Eurasia Nonproliferation Program at the James Martin Center for Nonproliferation Studies. “The Iranians are accruing benefits from this change. The nature of their relationship has gone beyond just getting things. There’s knowledge transfer, there’s intangible gains.”

Intelligence officials described Russia as “advancing” agreements negotiated in secret to supply Iran with Su-35s, one of Russia’s most capable fighter-bombers and a potentially dramatic upgrade for an Iranian air force that consists mainly of rebuilt U.S. and Soviet aircraft dating from before 1979. Russia also pledged to provide technical help with Iranian spy satellites as well as assistance in building rockets to put more satellites into space, the officials said.

There is no public evidence that Su-35s have been delivered; the holdup may be a delay by Iran in paying for the planes, according to a U.S. and a Middle Eastern intelligence official with detailed knowledge of the deal.

On the defensive side of the ledger, Iran has long sought Russia’s top-of-the-line antiaircraft missile batteries to protect its nuclear and military facilities against a possible U.S. or Israeli strike. In 2007, Tehran cut a deal to purchase Russia’s S-300 antiaircraft system, but Moscow delayed supplying the weapons amid pressure from the United States and European powers. The self-imposed ban ended in 2016, and Iranian S-300s became operational in 2019.

Iran has since sought to purchase Russia’s more capable S-400 system, although whether Moscow has moved to provide S-400 batteries is not publicly known.

Some variants of the S-400 are equipped with radars that can defeat stealth technology used by modern warplanes. Russia has deployed the S-400 to protect its military bases in Syria, and the batteries constitute a potentially lethal threat to U.S. and Israeli military aircraft that occasionally operate in Syrian airspace.

An Israeli airstrike on Iran’s consulate in Damascus on April 1 killed two Iranian generals and led directly to Iran’s decision to launch drones and missiles against Israel over the weekend.

Lt. Gen. Herzi Halevi, the Israel Defense Forces chief of staff, said Monday that Iran’s attack “will be met with a response.”

If delivered, the new Russian antiaircraft missiles and anti-stealth systems, deployed to protect underground bases carved in rocky mountains, would assuredly make Iranian airspace “a more dangerous place,” said Can Kasapoglu, a senior fellow with the Hudson Institute, a Washington think tank.

“This is important at a time when the regime is fast and unchecked moving toward a bomb,” Kasapoglu said. In addition, he said, “any engagement [with Israel] will take place in the Iranian airspace where Tehran will hold the advantage of playing at home.”

Moscow also is reaping benefits from the collaboration, intelligence officials said. In addition to thousands of drones procured from Iran, Russia agreed late last year to purchase about $2 billions worth of additional military goods, including anti-drone defensive systems that have become a top priority for Russian generals in Ukraine, according to two intelligence officials with detailed knowledge of the deal.

Iran has separately agreed to sell Russia surface-to-surface missiles for use in Ukraine and, according to a new intelligence assessment, is expected to begin transfer of the weapons imminently. Spy agencies have seen no evidence so far that the missiles have been delivered, the officials said.

The production of battlefield drones, meanwhile, has evolved into a joint venture between the two countries, intelligence officials said. Initially, Iran’s provision of drones to Russia was an attempt by Tehran to help its ally plug a hole in its military campaign against Ukraine. Russia, which possessed few battlefield drones at the start of the war, began using two types of Iranian-made Shahed drones in the fall of 2022: the long-range, sweptwing Shahed-131 and Shahed-136.

By midsummer 2023, Russia was beginning to manufacture Iranian-designed Shahed-136 drones indigenously, at factory in Alabuga, a town in Russia’s Tatarstan region, about 500 miles east of Moscow. Russian documents obtained by The Washington Post last year described plans to manufacture 6,000 drones by summer 2025 to use in its campaign of strikes against Ukrainian forces as well as electricity plants and other vital infrastructure.

Concerned about Russia’s domestic production, the Ukrainian military launched a drone attack of its own against the Alabuga complex on April 2.

More recently, Moscow and Tehran have begun working cooperatively on new kinds of unmanned aerial vehicles, or UAVs, according to intelligence officials and leaked documents. The trove of Russian and Iranian emails and records released by the hacking group Prana Network were purportedly stolen from an Iranian server linked to Iran’s Islamic Revolutionary Guard Corps earlier this year.

Among the documents were details of visits by Iranian and Russian delegations to tour weapons facilities in both countries. The Iranians’ trip to the NPP Start factory was described in a Russian “program” for the visit that listed tours of defense facilities in five cities. The document was signed by officials of Technodinamika JSC, which operates NPP Start, as well as the Russian Ministry of Defense.

The Post could not independently verify the documents, but two Biden administration officials acknowledged that U.S. intelligence agencies have closely studied the leaked materials and do not dispute their authenticity. Neither Russia nor Iran have publicly responded to the leak.

Several documents describe an April 2023 trip to Iran by a delegation of Russian engineers to watch a demonstration of a new jet-powered drone as well as a line of hunter-killer UAVs designed to destroy enemy drones. Both appeared to impress the visitors.

Two variants of the jet-powered drone, dubbed the MS-237 and Shahed-238, were described as having a maximum speed of nearly 400 mph - about three times faster than previous iterations of Iranian drones. Tehran revealed the existence of the new drone at an air show in November.

In the demonstration, the jet drone - code-named “motorboat” in the Russians’ internal communications - “successfully took off, accomplished the tasks … and successfully landed by parachute,” a leaked Russian report said. “Given its high speed, the boat is essentially a cruise missile.”

The test apparently helped cement an agreement to acquire more than 600 of the Iranian-designed jet drones, with most of them built on Russian soil with Iranian parts and help, according to the leaked emails. The documents also describe protracted negotiations over how Russia would pay for the drones. At least two installments were to come in the form of gold bullion valued at about $140 million, the documents show.

In January, photos of the remains of a jet-powered drone that appears identical to the MS-237 were posted by Ukraine bloggers after the aircraft reportedly was shot down somewhere over central Ukraine. It is not yet known whether any of the jet drones were launched against Israel in the recent Iranian attack.

“It’s faster, which means it is more difficult to intercept,” said Fabian Hinz, a defense analyst and expert on UAVs and missile systems with the International Institute for Strategic Studies, a London-based think tank. But, he said, the jet drones are “probably also substantially more expensive, because these types of jet engines are tricky to build.”

Producing the drones as a joint production offers substantial benefits for Iran, including the ability to evaluate their performance on Ukrainian battlefields. David Albright, an expert on Iran’s weapon systems and president of the Institute for Science and International Security, a Washington nonprofit, noted that the leaked documents show evidence of Russian engineers incorporating design improvements on Iranian drones.

“Mistakes and flaws in the designs will be identified and fixed,” he said, “and Iran would benefit from that.” Even if Russian systems such as the S-400 have not already been sold to Iran and deployed there, Albright said the sharing of design information and technological expertise could quietly bolster Iran’s capabilities without triggering alarms in the West.

“You might not see anything,” he said.

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