There have been a lot of sketchy claims made about the long-delayed, over-budget F-35 Joint Strike Fighter, history’s most expensive weapon program. But this one takes the cake. According to Stephen O’Bryan, a vice president at F-35-maker Lockheed Martin, the radar-evading jet fighter will actually get stealthier over time — without any upgrades.

To be clear, every other stealth warplane has steadily lost its ability to dodge enemy radars owing to wear and tear on the plane’s special skin coating. Not so the F-35, O’Bryan said.

In the latest issue of Air Force magazine, O’Bryan insisted the single-engine JSF, which is projected to cost $1 trillion to develop, buy and maintain, is fundamentally different than its predecessors. “The surface material smooths out over time, slightly reducing the F-35’s original radar signature, according to the Lockheed Martin official,” John Tirpak  wrote.

With the older F-22, B-2 and F-117 stealth warplanes, the opposite happened. All three of the previous models saw their surfaces gradually degrade and all required expensive upgrades just to maintain their radar-avoiding qualities at the original levels. In light of other empty promises Lockheed has made regarding the F-35, it’s highly unlikely the new jet will buck this historical trend.

Looking back, the 59 Lockheed-made F-117s, retired in 2008, was by all accounts a nightmare to maintain — a consequence of its 1970s-vintage technology. The F-117 owed its stealthiness to its angular shape, putty and later tape to cover radar-reflective seams in the fuselage and an external coating of radar-absorbing material.

The F-117s were hand-built by Lockheed, each to a slightly different design with varying levels of stealth. Maintaining them was said to be more of an art than a science. Over time, that only increased the jets’ differences — and their visibility to sensors. Starting in 1999, the Air Force spent roughly $1 million per plane to normalize the fleet. “Standardizing the configuration will preserve radar cross-section performance,” the Federation of American Scientists explained.

The 21 B-2s, manufactured by Northrop Grumman in the late ’80s and ’90s, were based on more sophisticated technology than were the F-117s, with smooth surfaces replacing the sharp angles. But like the F-117s, the larger B-2s lost their radar-defeating edge over time. In particular, the radar-absorbing material surrounding the B-2′s engines cracked and disintegrated in the extreme heat of the jet exhaust, compromising the bomber’s stealth. In 2010 the Air Force Research Laboratory demonstrated a new composite material meant to better resist the heat.

Likewise, the 187 F-22s that Lockheed built for the Air Force ending this year also required upgrades just to maintain their elusiveness. A Washington Post investigation in 2009 found that the F-22s’ radar-absorbing coatings could be damaged by rain — a claim the Air Force denied.

In any event, “the number of maintenance personnel required to maintain the F-22A’s specialized stealth exterior has increased, posing a continuing support challenge for this aircraft,” the Government Accountability Office warned in May. Now the Air Force is installing new, more robust stealthy components under the $1.3 billion Reliability and Maintainability Maturation Program.

Lockheed’s O’Bryan told reporter Tirpak that the F-35′s advanced technology will reverse this trend of gradually eroded stealth. In contrast to old-style coatings, “the conductive materials needed to absorb and disperse incoming radar energy [on the F-35] are baked directly into the aircraft’s multilayer composite skin and structure,” Tirpak reported, citing O’Bryan.

Over time the JSF’s skin will settle, O’Bryan boasted, making it even smoother and more radar-evasive — all without any of the expensive upgrades required by previous stealth planes.

The F-35, of which the Pentagon plans to buy more than 2,400, is a brand-new design that’s still only part-way through testing, so it’s impossible to verify O’Bryan’s claim. Only time will tell for sure.

But it’s worth noting the extreme pressure on O’Bryan and other Lockheed execs to extol, even exaggerate, the F-35′s capabilities. When JSF development began around 15 years ago, only the U.S. possessed stealth warplanes. But today Russia, Japan and most notably China are also working on their own radar-defeating models. It’s no longer enough for the F-35 to merely duplicate the skills of older U.S. stealth jets; it must significantly improve on them in order to stay ahead of foreign rivals. In this context it’s not hard to see why O’Bryan would promise the impossible, or at least improbable.

That said, Lockheed officials have made unlikely  claims before. Back when the F-35 was still on the drawing board, the firm said the new plane would perform better than conventional fighters such as the F-16 — and would be cheaper, to boot. Neither claim turned out to be true. Nor did the F-35 enter service in 2008, as originally promised.

So when O’Bryan insists his company’s new stealth fighter will dodge a problem that has vexed every previous radar-evading jet, it’s wise to be very, very skeptical.