The cheapest unit available in AWBW, Infantry are nonetheless an incredibly important unit and should not be overlooked.
Usage
An Infantry's primary function lies in the fact that, apart from Mechs, it is the only unit capable of capturing properties on the map. See Capturing for more details.
The secondary function of infantry is to block your more valuable units from being attacked. While weak defensively, infantry can usually take at least one attack from most direct combat units before being destroyed. This prevents the opponent from hitting more valuable units in the process, and also potentially leaves them open to a counterattack from your defended units.
Infantry are also effective at blocking certain tiles that you do not want your opponent to take control off, such as cities or other tiles with high defense ratings. Infantry can block air units from flying over them as well.
A common strategy is to have a group of infantry backed up by Tanks and Artillery to gain control of an area, making it difficult for an opponent to attack without suffering a heavy counterattack before they can break through the infantry line.
The final use of Infantry is a last-ditch attacker. The Infantry's Machine Guns do minimal damage to most non-infantry targets, but can usually take off 1 HP from lighter-armored units such as Tanks and B-Copters. Be aware that attacking a full-HP Tank will result in your infantry taking much more damage from the counterattack in the process. Infantry are, however, good at finishing off 1 HP units when more valuable units are unavailable or would be put to better use on other targets.
Fighting Against
On their own, Infantry are of little threat to anything but other foot soldiers. In a match between foot soldiers, whoever gets the first strike will generally come out the clear winner, though defending Infantry on mountains will typically come out even against attacking Infantry that are on lower-defense terrain.
Grouped with other, stronger units, however, Infantry become much more dangerous, as they can block unit movement and put attackers in unfavorable positions. They can even completely surround units and prevent them from moving.
When fighting against Infantry supported by other units, it is advisable to only focus on the Infantry that can and need to be removed in order to expose their more valuable units, ignoring other Infantry until the larger threats have been eliminated.
Anti-Airs are particularly strong against Infantry. A full-HP Anti-Air is guaranteed to OHKO an infantry on a road, and with any offensive boost at all, will OHKO infantry on plains as well, quickly opening up an infantry line and allowing you to hit more valuable units.
Most lower-tier units will also do heavy damage to an Infantry as well, but will likely take more than one hit to destroy them. Any unit spent attacking Infantry over other units where plausible hurts an army's overall attack power, so care must be taken on how many Infantry to attack in the middle of battle.