Communication Towers (Com Towers for short) are a kind of Building and Terrain in Advance Wars: Dual Strike and Advance Wars: Days of Ruin. While Comm Towers lack the ability to heal or refuel Units which stay on them, capturing a Com Tower increases the power of the player's Units:
Attack by 10% in Dual Strike, both Attack and Defence by 5% each in Days of Ruin.
Gaining or losing a tower thus can make a large difference, especially when outnumbered and every unit counts.
Green Earth CO Javier gains an additional 10% Attack and Defense for every Com Tower under his control. His CO powers increase their bonus even further, doubling it with his Normal CO power and tripling it by using his Super CO Power, making his units virtually invincible. When no towers are under his control, these effects are essentially useless (barring the other effects of his CO Powers).