War Wings-How to get a higher tier plane? What’s the Plane Tech Tree?-[War Wings English Guide]

According the advancing level, planes are divided into nine tiers. Complete the tech tree between two tiers by using RP and you can unlock the next level aircraft, then you can purchase the aircraft as long as you have enough silver and RP. Every branch of the tech tree has its feature and the plane with higher tier will carry on its feature as before.