: This XP is first used to unlock specific modules—such as better guns, engines, and turrets—before the next tank in the line can be researched.

Unlike premium vehicles, "normal" (tech tree) tanks require a dedicated research process:

The core of "Normal Tanks" on PSN (PlayStation Network) revolves around the experience, which offers a free-to-play tactical combat loop where players progress through tiers of historical and modernized armored vehicles. The Progression Loop: Research and Development