Fortress Arena is the upgraded version of "Fortress V2". 
They did not only add blockchain elements to Fortress V2 but formed an ecosystem around the token to provide utility and motivation for players. 

Fortress Arena is a P2E (Play to Earn) game and combines the NFT elements of the blockchain. 
Players will initially need to own a tank (NFT) to start the game. 
New tanks (NFT) can be created through the R&D center. 
Players can earn TANK tokens by winning in a PvP match or clearing stages. 
Damaged tanks (NFT) must be repaired at the repair shop. TANK Token Stakers will get the authority to operate the repair shop. 

All Tank-NFTs have unique characteristics, similar to human genes. This is why we call them "unique tanks". 
The players can combine their tanks (NFT) into 2 tanks at the R&D center. 
When 2 tanks are combined, there is a chance of obtaining an advanced tank. 
The more advanced the tanks, the better the stats and special effects that are added to the Tank-NFT card.