Operation: Firestorm is an enhancement mod for C&C Generals: Zero Hour. This mod currently features 8 unique playable Generals each with a huge arsenal of new units, buildings and special powers ar their disposal. While the core gamplay stays the same, a number of interesting new gameplay mechanics are added. In addition the overall visual quality is greaty improved, including new models, textures, FX and an improved User-Interface, available in full-HD resolution.
The Infected (or you might just call it Zombie) is a basic melee unit and is not directly trainable.
Instead, these units are created by transforming your Volunteers for a small cost.
Alternatively, a rank 5 General's Power allows you to transform enemy infantry and even vehicle crew into Zombies which follow your command.