The US and its allies continue to invest heavily in the F-35 and other stealth-capable aircraft. But Russia and China are rapidly developing systems that would negate the benefits that stealth offers.

According to Zarchary Keck writing in The National Interest, both Beijing and Moscow have begun development of unmanned aerial vehicles that have the goal of finding, detecting, and possibly even eliminating enemy stealth aircraft.

China's stealth detection drone, called the Divine Eagle, is believed to be specially built to counter stealth aircraft while they are still far from the Chinese mainland.

Popular Science notes that the drone's "long range anti-stealth capabilities can be used against both aircraft, like the B-2 bomber, and warships such as the DDG-1000 destroyer ... the Chinese air force could quickly intercept stealthy enemy aircraft, missiles and ships well before they come in range of the Mainland."

The Divine Eagle features multiple different radar systems, including X/UHF low band radar systems, according to Popular Science. These systems could be used to track stealth aircraft like the F-35 at long distances, as most stealth technology is created to avoid high band radar systems, thereby eroding one of the key advantages of the fifth-generation plane.

The Divine Eagle has apparently undergone multiple redesigns which sought to limit the plane's infrared signature — something that would help ensure the drone's own purported stealth capabilities.

Russia has been working on its own stealth-detection drone. Flight Global writes that the Russian military subcontractor KRET debuted a stealth drone prototype at the MAKS air show in Moscow in August.

The unnamed drone, Flight Global notes, will also come outfitted with UHF and X-band radar systems that could be used to detect stealth aircraft. Additionally, the drone is outfitted with an electronic warfare system that would both cloak the drone and make it difficult to target with air-to-air missiles.

If such Chinese and Russian systems are ultimately proven effective, the US' reliance upon stealth technology will need to be radically evaluated.

At the same time, both Chinese and Russian claims of the technology's status should be viewed with some skepticism.

Chinese military technology is often based on designs stolen from US and other allied countries, which calls Beijing's domestic research and development capabilities into question. Additionally, rampant corruption throughout the Chinese military may undermine the country's ability to fight or develop advanced technologies.  

Russia also faces serious challenges to its military ambitions. Large-scale economic problems throughout the country — the partial result of EU and US sanctions stemming from Russia's aggressive policies in Ukraine — have limited Russia's military procurement. Already, Russia is cancelling the construction of most of its planned next-generation tanks and may have be scrapping of plans for a fifth-generation bomber. Any new stealth drone could face similar funding hurdles.

Still, the potential rise of anti-stealth drones should worry the US, as it could expose an over-reliance on stealth technology that suddenly has far less tactical and strategic worth.

Some in the Pentagon already feel that way. In February, Chief of Naval Operations Adm. Jon Greenert gave a speech in which he called out the potential limitations of stealth technology.

"You can only go so fast, and you know that stealth may be overrated," Greenery said. "Let's face it, if something moves fast through the air, disrupts molecules and puts out heat — I don't care how cool the engine can be, it's going to be detectable. You get my point."