Other than astronomically high procurement and operating costs, Washington’s plans to sell the Indian Air Force (IAF) F-35 Lightning II stealth fighters pose a major operational and technical vulnerability that the US itself acknowledges and fears – Russian Almaz-Antey S-400 ‘Triumf’ self-propelled surface-to-air missile systems, which the IAF has so far deployed three batteries of and awaits delivery of another two later this year.
For the US, the S-400 poses a ‘real and credible’ threat to the Lockheed Martin-designed and series-built single-engine F-35s because of its multiple advanced radars that are capable of detecting stealth aircraft, drones and even ballistic missiles at long range. In fact, so great is the US apprehension over the S-400s, that in July 2019 it removed North Atlantic Treaty Organisation (NATO) ally Turkey from its F-35 programme, canceling its order for 100 of the 5th generation stealth fighters after Istanbul installed two Triumf regiments, which it had acquired from Russia for $2.5 billion.
The US’s primary concern, and one which seemingly endures, is that the S-400 could compromise the F-35’s security. Consequently, in late 2020 President Trump’s administration sanctioned Turkey’s Presidency of Defence Industries (SSB) under the Countering America’s Adversaries Through Sanctions Act (CAATSA) and imposed restrictions on key figures in Istanbul’s defence sector.
These embargoes also included a ban on the export of specific US military technologies and products and blocked several of Turkey’s targeted entities and individuals from accessing US financial institutions. Late last year Turkish President Tayyip Erdogan had called upon Washington to lift these sanctions as they hindered defence purchases and bilateral trade between NATO allies but to no avail.
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The S-400, one of the world’s leading air-defence missile systems, employs multiple advanced long-range surveillance, target acquisition, and engagement radars designed to detect and track low-observable stealth aircraft like F-35s. These include high-frequency L-band and S-band radar which can monitor low-observable targets by identifying and pinpointing their radar from different angles, alongside X-band control radar that is for subsequent target engagement with the S-400s multiple missile variants, with estimated strike ranges of between 120-400 km.
Additionally, the US’s biggest fear is that the S-400s could gather data on the F-35’s radar signature and behaviour which, in turn, could be used to further improve the air defence systems’ ability to track and target the fighter more effectively, thereby compromising its stealth advantage developed at great expense.
Furthermore, the S-400 can also be integrated into wider air defence networks, allowing it to share target information with other missile systems, fighter aircraft, and related radar systems by eliminating blind spots and making it harder for stealth combat platforms to operate effectively. Military experts said such multi-layered air defence networks could potentially augment the F-35’s overall vulnerability and operationally limit its freedom of movement should this sensitive information be disseminated, especially to the Russians, who may well pass it on to the Chinese.
Conversely, to counter the S-400’s capabilities, the F-35 relies on its Electronic Warfare (EW) systems to jam or deceive ground air defence radar and mission planning and intelligence to avoid Triumf deployments. The fighter can also resort to Suppression of Enemy Air Defences (SEAD) operations to target and destroy the S-400 before it can engage its aerial target. Additionally, F-35s can evade detection by decreasing their radar cross-section, which serves to ‘confuse’ the S-400 as part of what in recent years has emerged as the cat-and-mouse contest worldwide between stealth fighter technology and of advanced air-defence systems.
Meanwhile, the F-35 on display at the recently concluded Aero India 2025 in Bengaluru – which coincided with Prime Minister Narendra Modi’s day-long Washington visit – reinforced the US intent to sell this fighter to the IAF. “We’re paving the way to ultimately provide India with F-35 stealth fighters” Trump arbitrarily stated at the joint press conference with Modi in Washington on February 13.
Startled Indian officials responded by declaring that no ‘firm proposal’ existed as yet to acquire the F-35 but privately admitted that Delhi was under ‘great pressure’ to acquire US-origin fighters for the IAF under its plans to make up depleted fighter squadron numbers. In recent years, India’s combat squadron strength dropped to around 30, instead of the 42 mandated by the government to effectively meet the two-front collusive threat from Pakistan and China. These squadron numbers will decrease even further as two legacy MiG-21’Bis’ ground attack fighter squadrons are up for ‘number-plating’, or retirement, this year.
It is not clear how Trump intends to reconcile his steadfast and resolute salesmanship with US apprehensions about the IAF’s S-400s gathering data on the F-35s radar signature and related information, from where it could conceivably find its way to the Russians and possibly even China. As noted, this trepidation has been one of the US’s abiding concerns and the sole cause for Washington terminating Turkey’s F-35 deal six years ago.
After all, the IAF has already taken delivery of three S-400 systems it ordered in 2018 for $5.5 billion and deployed them along the western and northern borders with Pakistan and China. And last October, Air Chief Marshal A P Singh told reporters at his annual presser that the remaining two S-400 systems would be delivered later in 2025, all of which technically posed a ‘collective threat’ to the F-35s, in the event of the IAF opting for them, along with the real possibility of an information leak to close ally Russia.
In short, the solution to the predicament of F-35’s operating alongside S-400s for now, remains elusive.
