Key Points and Summary – In 2022, viral photos of “rusty” F-35s on a U.S. carrier kicked off a media firestorm—but the jets themselves were never in danger.
-The F-35’s structure is aluminum, titanium, and composites, none of which rust. What discolored was microscopic iron in the outer radar-absorbent coating, a cosmetic issue with no impact on performance or stealth.
F-35 Fighters Ready. Image Credit: Creative Commons.
Two Dutch F-35 Lightnings patiently wait for their opportunity to maneuver into position to receive more fuel mid-air from a KC-135 Stratotanker over the Arctic Circle, May 31, 2023. The 101st ARW is taking part in Arctic Challenge Exercise 2023, a live fly exercise that serves to advance arctic security initiatives and enhance interoperability in the increasingly dynamic and contested region.
-Unlike earlier stealth jets that rely on fragile tapes and epoxies, the F-35 has RAM baked into ultra-precise composite panels with hairline seams.
-Tests on a battered full-scale test article showed virtually no change in radar signature. Lockheed has since tweaked the topcoat to prevent future staining.
No, the F-35 Isn’t Rotting on the Flight Deck – The Real Story Behind the “Rust”
In 2022, when pictures of rusty F-35s sitting on the flight deck of an American aircraft carrier hit the internet, they prompted a wave of hyperbolic news articles and social media tirades from political pundits.
But then the story seemed to just… go away.
Like a lot of stories that get tons of attention and then fizzle out, this story went away because it was entirely predicated on misinformed knee-jerk reactions to something most people just didn’t understand.
The F-35 is almost entirely made out of aluminum, titanium, and carbon composites, none of which can actually rust. So, the first thing you need to know about those rusty F-35s is that the rust we can see never had a chance at compromising the jet’s actual performance.
The rust was only paint deep, because what we see oxidizing in these pictures is actually microscopic iron ferrite in the outermost layers of the F-35’s radar absorbent coating.
All stealth aircraft are coated in radar-absorbent materials, or RAMs, which can be produced in different ways and with different ingredients to absorb very specific types of electromagnetic radiation (or radar waves) and then dissipate them as heat, rather than reflecting them back at the broadcasting array.
The RAM coating on America’s stealth fighters has been said to be capable of absorbing upwards of 80% of inbound radar waves, and former Skunk Works director Ben Rich famously attributed about 35% of a stealth fighter’s stealth to this advanced coating.
This coating is particularly important anywhere there are seams between body panels, for example on the leading edges of the wings, around jet inlets, and anywhere else that’s likely to produce a sizable radar return.
F-35 Near the Flag. Image Credit: Creative Commons.
F-22 and F-35 and the Flag. Image Credit: Creative Commons.
However, the F-35 takes a very different approach to its RAM coatings than previous stealth jets like the F-22 Raptor or B-2 Spirit.
Those older stealth jets have layers of RAM in the form of tape, epoxies, and liquid spray applied to them after assembly; but the F-35 has its base layers of RAM baked into the composite material of its body panels.
The F-22, B-2, and F-117 need to have RAM epoxy and tape painstakingly applied to every seam between thier body panels. But the F-35’s body panels are made primarily by incredibly advanced multi-axis robots, CNC machines using lasers to measure so precisely that the gaps between the panels are known to be somewhere in the neighborhood of 50 microns across… that’s less than half the width of a human hair.
In other words, the F-35’s body panels are not only radar-absorbent in themselves, but they’re also assembled with such precision that the radar-reflecting seams between them practically aren’t even there.
And there’s data to support this claim. Before the first F-35 entered service, Lockheed Martin built what it called a “highly detailed, full-scale Signature Measurement Aircraft (SigMA),” with all the same RAM coatings found on the production F-35. The SigMA aircraft was then put in front of a radar array to get a baseline measurement of the jet’s radar cross section.
F-35A Lightning II’s from the 34th Fighter Squadron at Hill Air Force Base, Utah, land at Royal Air Force Lakenheath, England, April 15, 2017. The aircraft arrival marks the first F-35A fighter training deployment to the U.S. European Command area of responsibility. (U.S. Air Force photo/Tech. Sgt. Matthew Plew)
F-35 Beast Mode. Image Credit: Lockheed Martin.
Then, it was subjected to extreme abuse comparable to more than 600 operational flight hours (which, depending on the aircraft, is about three years’ worth of use).
Finally, three dozen more significant paint defects were added, representing the sort of damage that might happen on a busy flight deck, but that would all but certainly be repaired once identified.
The beaten-and-battered Sigma aircraft was returned to the same radar array for a new radar cross-section measurement, and it was found to be pretty much as stealthy as it was at the start.
It turns out, that top layer of RAM coating doesn’t really do any of the heavy lifting when it comes to stealth.
But, that doesn’t change the fact that rusty jets are a bad look, so Lockheed Martin set to work changing the formula of that top layer of coating to prevent the rust discoloration from happening anymore.
The new F-35 Lightning II stands on display at the First Aircraft Arrival ceremony on Nov. 2, 2024, at Naval Air Station Joint Reserve Base Fort Worth, Texas. The delivery of the F-35 ushered in a new era of modern-day warfighting for the U.S. Air Force. (U.S. Air Force photo by Staff Sgt. Richard Moser)
Now every new F-35 that rolls off the line will be rust-free for the foreseeable future.
As for the older jets, they’ll just receive the new top coating during their next scheduled maintenance.
About the Author: Alex Hollings
Alex Hollings is the editor of the Sandboxx blog and a former U.S. Marine that writes about defense policy and technology. He lives with his wife and daughter in Georgia.
