India’s Radar Tracked British F-35 Over Arabian Sea: The Truth Behind Stealth, Luneburg Lens, and Modern Detection Capabilities

In a significant demonstration of its airspace monitoring capabilities, the Indian Air Force (IAF) successfully tracked a British Royal Navy F-35B stealth fighter as it flew over the Arabian Sea and later made a precautionary emergency landing at an airfield in Kerala. The episode — which reportedly became visible in radar and surveillance images — has sparked discussion about the true nature of stealth technology, the role of Luneburg lenses on F-35s, and the evolution of radar systems designed to counter stealth aircraft.

How India Tracked the F-35

The F-35B, operating from the Royal Navy’s aircraft carrier in the region, was reportedly on a routine sortie when it experienced a technical fault, prompting a diversion to Kerala. Indian air defense radars detected and continuously tracked the jet as it entered Indian airspace — an occurrence that, at first glance, might seem surprising given the aircraft’s reputation as one of the most advanced stealth platforms in service today.

The primary reason for this tracking success lies in the presence of a Luneburg lens — a small radar reflector intentionally installed on stealth aircraft during peacetime and transit operations. This device creates a larger radar signature, allowing friendly and civilian radar systems to safely monitor the aircraft’s position. In essence, the lens acts as a radar beacon, ensuring air traffic control and allied forces can keep tabs on the jet without confusion or risk of collision.

When images of the grounded F-35 in Kerala surfaced, observers noted the distinctive bulge where the Luneburg lens is typically mounted, confirming that the jet was not operating in a full stealth configuration at the time.

F-35: Stealth, Not Invisibility

It’s important to clarify that the F-35 is not invisible to radar. Stealth technology is designed to reduce an aircraft’s radar cross-section (RCS), making it harder — not impossible — to detect and track. The F-35 employs shaping, radar-absorbent materials, and coatings to deflect and absorb radar waves, significantly shrinking its apparent size on enemy radar screens.

However, modern air defense radars — including those operated by India — are increasingly equipped to counter stealth tactics. Radars working in VHF, UHF, and L-band frequencies, which have longer wavelengths, are less affected by the shaping techniques used in stealth designs. These longer wavelengths can create returns even from stealth aircraft, albeit often at lower resolution or accuracy.

Next-generation radar systems, like India’s indigenous ‘Ashwin’ long-range tracking radar, and upgrades to existing Russian-origin platforms such as the Nebo-M, are designed to provide early warning of low-observable aircraft. When fused with data from multiple sensors — including passive systems and infrared trackers — the overall picture improves, and stealth’s advantage diminishes.

The Role of Luneburg Lens in Peacetime Operations

The Luneburg lens is a safety feature, not a weakness. In routine missions or during operations over friendly or neutral airspace, stealth aircraft usually fly with Luneburg lenses attached. This ensures civilian and military air traffic controllers can monitor the aircraft. When transitioning to combat conditions, the lens can be quickly removed or retracted, restoring the aircraft’s low observability.

In the case of the British F-35B, the lens would have been in place precisely to ensure the jet could be tracked during an emergency or unplanned interaction with foreign airspace — which is exactly what occurred as it diverted to Kerala.

The Evolving Game of Stealth vs. Radar

The incident highlights a broader truth: stealth is not a cloak of invisibility. Instead, it’s one component of survivability, working best when combined with tactics, electronic warfare, and situational awareness. Meanwhile, radar and sensor technology are advancing rapidly. Multi-band radar networks, passive detection systems, and artificial intelligence-enhanced data fusion are narrowing the gap, making even the most advanced stealth aircraft more vulnerable to detection.

For nations like India, which faces the prospect of stealth aircraft in neighboring air forces, investments in anti-stealth radar technologies and integrated air defense networks are crucial — and evidently, already paying dividends.

Conclusion

The ability of Indian radar systems to track the British F-35B during its emergency diversion underscores the realities of stealth technology. While the F-35 is a marvel of engineering, it is not invisible. The Luneburg lens — deliberately designed to make the aircraft visible — played a key role in this case. At the same time, modern radar systems continue to evolve, ensuring that the balance between stealth and detection remains a dynamic and ongoing technological contest.