章 406: Chapter 202: Stealth Aircraft_3

With the experience from previous upgrades, Yan Fei knew that once he had completed selecting the Drone Upgrade Template and scanned it, there would be subsequent requirements: the Upgrade Materials. The materials needed for each drone upgrade varied greatly from one another. However, one thing was very certain—that there were items indispensable for the drone upgrade, known as the Upgrade Essential Items.

In the past, Yan Fei went through great lengths to barely obtain two Upgrade Essential Items for the drone. To meet the requirements for this upgrade, he needed three such items. This meant that even if all other upgrade conditions were met, Yan Fei still had to find the third Upgrade Essential Item to carry out this drone upgrade operation.