Here are some ideas. Please give feed back if they are too Over powered / Under powered.

Warship This class branches off Destroyer at level 45. It shoots triangles that will continue moving forward and fade away like normal bullets. But if they come in range of another tank, they will home in on it and hit it. https://docs.google.com/drawings/d/10c3TJuzWrNJOUtJsGZi0XfXEqc5fy7Y62izpbT8Emu8/view

Controller This class branches off Overseer at level 45. It controls one dark blue hexagon that cannot be destroyed. The hexagon gets bigger the more reload and takes less knock back the more penetration. It hits really hard but when it hits, it get knocked back to the controller. It would not be very fast, though. https://docs.google.com/drawings/d/1R-CPROFXSamYwznlDBIywJo2bm4PU41qhpMHB7_0D5o/view

Flamethrower (Note: Inspired by non-in-game class. I couldn't find the name of the original person. Sorry!) It would branch off gunner at level 45. It would shoot a ton of small bullets. By a ton, I mean like a lot more than Pentashot. https://docs.google.com/drawings/d/1J_J--uiWFkEH20ClQJh6DJnkNfnQrYZAjb0SI5m_EhQ/view

Also, I know this is popular but it would be amazing if you added a mini-tank controlling class. :D