China may have found a new use for old fighter jets: turn them into combat drones.

Some experts fear that masses of these robotic jets could saturate Taiwan’s air defense as the prelude to a Chinese invasion.

The J-7 (NATO code name: “Fishcan”) is China’s copy of the 1960s-era Soviet MiG-21. Despite originally being a mid-Cold War design, more than 2,400 J-7s were produced in 54 variants all the way up until 2013 (Pakistan and Iran still fly the F-7 export version). The People’s Liberation Army Air Force (PLAAF) has almost 300 J-7s, according to an annual report on military capabilities and defense economics from the International Institute of Strategic Studies.

But with China receiving new fourth- and fifth-generation fighters—such as the Russian-designed Su-30, plus the J-16 and the J-20 stealth fighter—the third-generation J-7 is long past its prime. China may completely retire the aircraft in 2023, according to the state-sponsored Chinese newspaper Global Times.

In the U.S., obsolete combat aircraft end up mothballed in the boneyard, or converted into target drones, as became the F-4 and F-16 fighters. But Global Times suggested a different fate for the J-7: the aircraft “could be modified to become drones and play new roles in modern warfare.”

That “new role” may very well be converting the J-7 into an unmanned combat air vehicle (UCAV). This isn’t the first time a jets-to-drones plot has arisen; there has been previous speculation that China might convert the J-6—China’s copy of the 1950s-era Soviet MiG-19 fighter—into a UCAV.

But observers were quick to note that in 2021, four J-7s joined a group of newer J-16 fighters during exercises near Taiwanese airspace, an unusual step for an aging aircraft that even the Taiwanese dismiss as a “grandpa jet.” Some wondered whether these J-7s had been converted into drones, though no evidence has been made public.

Why convert a manned fighter into an unmanned combat drone? The most obvious reason would be not to waste expensive jets. But a bigger reason might be performance. Purpose-built strike drones like the U.S. MQ-9 Reaper or Turkish TB2 Bayraktar have a maximum speed of around 130–300 miles per hour, and tend to be clumsy, propeller-driven flying machines. A J-7-turned-drone could fly at almost Mach 2, and manned fighters are designed for agile, high-speed maneuvers. Combat jets can also heft a wide variety of ordnance, including air-to-air, air-to-ground, and anti-ship missiles as well as bombs.

“The cost of converting legacy aircraft into UCAVs is relatively low, but they retain many of their manned-variant characteristics,” concluded a 2022 study from the Mitchell Institute, a U.S.-based think tank, regarding the Chinese UCAV threat to Taiwan. “Converted airframes have the same performance, maneuverability, and payload capacity as the original platforms.”

Old J-6, J-7, and J-8 fighters, as well as Q-5 attack planes, could be converted into UCAVs and then “used as a means to overwhelm Taiwan’s air defense systems, to swarm an aircraft carrier, or carry out basic counter-air operations,” the Mitchell Institute warned. For example, China could dispatch hundreds of these UCAVs as the prelude to an invasion of Taiwan, with the drones depleting Taiwan’s supply of anti-aircraft missiles before manned strike aircraft go in.

“Like cicadas, which can remain underground for long periods of time, the PLAAF could choose to hide a large number of these UCAVs in underground shelters and have them surreptitiously emerge in mass for an attack on Taiwan,” per the study.

Ironically, the J-7 and other Chinese copies of Cold War-era Soviet aircraft might achieve more success as drones than they did with a pilot in the cockpit. Global Times described the J-7 as “the first supersonic fighter jet developed by China that can reach Mach 2.” In reality, the J-7 was based on MiG-21 blueprints and components delivered by the Soviets in 1961. When China and the Soviet Union split in the early 1960s over leadership of the Communist bloc, Moscow halted deliveries, and China reverse-engineered the design.

The J-7 did not have a sterling reputation, according to author Andreas Rupprecht in his book Dragon’s Wings. Problems included manufacturing defects, poor reliability, a flawed ejection seat, and a cockpit sized to fit Russian—rather than Chinese—pilots.

Recycling old jets into drones sounds thrifty. But the concept may have problems. Supersonic drones are in their infancy, especially supersonic UCAVs. Can a robot jet fighter perform high-speed combat maneuvers while being flown by a pilot with limited situational awareness in a ground station, rather than in the cockpit?

And while China may be able to get ample spare parts by cannibalizing some of these UCAVs, combat jets tend to require a lot of maintenance, especially a trouble-prone design like the J-7. It may be more economical just to build a lot of cheap drones.