China's Chengdu J-20. Chinese Military Review Six years after China's Chengdu J-20 strike aircraft made its first flight, the innovative jet has entered service with the People's Liberation Army's air force — and it exposes weaknesses in the US military in more ways than one.

On the surface, China's quick turnaround on the J-20 and other defense projects outpaces the US, where the F-35 Joint Strike Fighter, first flown in 2006, still struggles to meet operational requirements in its naval variant.

The J-20, which bears some resemblance to the US F-22, also raises questions about the extent to which China has been able to steal US military secrets.

Furthermore, China built the J-20 specifically to counter a weak point in the US Air Force: unarmed aerial refuelers and airborne early warning and control aircraft.

A senior scientist working on stealth programs told Business Insider the J-20's stealth wasn't all aspect or nearly as effective as its US counterparts. However, the J-20's stealth on the front end and its extremely long-range missiles make it ideal for knocking back US support planes and keeping the US Air Force away from the battle.

An F-22 refuels in flight. US Air Force/Airman 1st Class Kevin Tanenbaum

Peter Singer, a strategist at New America and author of "Ghost Fleet" — a novel that depicts a World War III situation with China, Russia, and the US — told Business Insider that this fits with a Chinese strategy called "assassin's mace."

According to Singer, in the Middle Ages, "Chinese assassins would carry a little mace under their sleeves" when facing a guard armed with a long sword.

Instead of the assassin carrying their own long, conspicuous sword to match the guard's strength, they used a mace designed to smash the guard's sword, turning the guard's strength into a weakness.

China's J-20 brings this ancient strategy into the modern world.

"These things you see as your strengths, we're going to invert that," Singer said, describing Chinese military doctrine.