China's J-20 stealth fighter lacks a gun, something which the US's stealth fighters made a point to include

Dropping the gun from the J-20 likely means its not useful as a dog-fighter, and that many older US jets could defeat it in head-on close range fights.

But the lack of gun also indicates a new focus for the J-20 which may be more modern and relevant to real aerial combat than even the US's F-22 and F-35.

China's J-20 stealth fighter jet represents a massive milestone for Beijing's armed forces and the first stealth aircraft ever fielded outside the US, but the impressive effort still falls noticeably short in some areas.

The J-20 doesn't have a cannon, and represents the only entry into the world of fifth-generation fighters that skips the gun, which has seen 100 years of aerial combat.

Enemy aircraft can't jam a fighter jet's gun. Flares and chaff will never fool a gun, which needs no radar. Bullets rip out of the gun already above the speed of sound and need not wait for rocket boosters to kick in.

While the F-22, the US's fifth-generation stealth superiority fighter can hold just eight missiles, its 20mm rotary cannon holds 480 rounds it can expend in about five seconds of non-stop firing.

The US's other fifth-generation stealth jet, the F-35, has already used its cannon in combat missions in Afghanistan.

But not every jet needs a gun, and not every jet needs to dogfight.

The J-20 Doesn't Even Consider Dogfights

The J-20's lack of a gun shows that the "Chinese recognise that being in a dogfight is not a mission that they're building for," retired US Marine Corps Lt. Col. David Berke, a former F-22 pilot and F-35B squadron commander, told Business Insider.

"They probably want to avoid a dogfight at all costs," he continued.

Business Insider previously spoke to air combat experts who said that the J-20 likely couldn't compete with even older US jets like the F-15 in head-on dogfights, but that the J-20 likely didn't need to.

The Chinese jet, with powerful sensors, long-range missiles, and a stealth design, poses a serious threat to US Air Force refuelling, early warning, and other support planes. Tactically, beating back these logistical planes with J-20s could allow China to keep the US operating at an arms length in a conflict.

But increasingly, it looks like the J-20 would lose handily to US fighter jets in outright combat, and that may be the point.

According to Berke, guns only work to around 800 feet to score aerial kills.

"I'd rather have a missile that's good to 800 feet that goes out to 20 miles than a gun that goes to 800 feet and closer but nothing else. ... Once you start getting outside of 1,000 feet, you can start using missiles," said Berke.

Because the J-20 wasn't meant as a close-in brawler, the Chinese ditched it. This will save room and weight on board the jet to allow for other technologies.

Also, the mission of the gun in air-to-air combat may be disappearing.

The US started building the F-22 in the 1990s with a hangover from combat losses to air-to-air guns in Vietnam after fielding jets without guns and relying solely on missiles. The F-35 includes a gun because it has a broad set of missions which include close air support and air-to-ground fires.

"In air-to-air, the cannon serves one very specific and limited purpose only useful in a very predictable phase of flight, which is a dogfight," said Berke.

"The Chinese probably recognise that [dogfights are] not where they want the airframe to be and that's not the investment they want to make," he continued.

"Utilising a gun against a highly manoeuvrable platform is an incredibly challenging task," Berke said. In World War II, propeller-driven planes frequently engaged in turning fights where they attempted to get behind each other and let the guns rip and bombers flew with turret gunners covering the whole compass.

But today's F-22s, J-20s, Su-35s, and other highly manoeuvrable jets give the guns an "extremely limited use" in combat, according to Berke.

Berke pointed out that the US likely has not scored an air-to-air guns kill in decades.