Although Engineers possess decent armour, they are normally unarmed, relying on commanders to clear the battlefield for them, or more likely, to be transported in APCs.
Engineers have two purposes:
1. To capture enemy structures. Depending on the health of the building, it can take up to five Engineers to break into a fully armoured enemy structure. A workaround is to damage the building until it hits red condition and then capture the building.
2. To repair own buildings. The engineer can bring a building instantly to full health. The unit disappears in the process, however.