The Infantry Center adds HP, ATK, DEF and Squad Size for Infantry Heroes. It requires Base level 11 for construction.
How the bonuses work
The bonuses apply to the Infantry hero type. The Squad Size stat concerns unit capacity associated with those heroes. It does not open another march slot; additional marches come from Squad buildings.
At Infantry Center level 10, the bonuses are 37 Squad Size, 5,000 HP, 248 ATK and 50 DEF. At level 30, they reach 100 Squad Size, 25,500 HP, 744 ATK and 150 DEF.
Wall of Honor
Infantry Center level 20 unlocks the Wall of Honor for Infantry Heroes. This is a distinct unlock alongside the building's normal stat progression. Infantry research also has Squad Size improvements, providing another route for developing that stat.
The Tank Center and Aircraft Center provide the corresponding bonuses for the other hero types. A center's name matters: its type-specific bonuses are not a general increase for every hero in a mixed formation.
