Engineseer in combat

"I hear the Machine Spirit's voice!"
Engineseers are low-ranking Techpriests of the Adeptus Mechanicus. Usually they maintain all technological assets of the Imperium of Man, and as such are working with most of Imperial institutes. Since "technological assets" happens to include war machines of Imperial Guard, lots of Engineseers are attached to Imperial Guard regiments and often risk life and limb operating directly on the battlefield, repairing damaged vehicles. However, Engineseers usually have bionic augmentations and are the only IG unit with Power Armor, and usually are surrounded with Servitors. For self-defense they carry a laspistol and a Power Axe (also their badge of office), and can also use their servo-arm (the manipulator hanging over his shoulder on the picture) in battle.
In Dawn Of War, Techpriest Engineseer is Imperial Guard's builder unit. Engineseers have the highest amount of hitpoints, ranged and melee weapons and repair vehicles or buildings four times as fast as other builders. He can also man Imperial Guard garrisoned buildings as effectively as a full squad of infantry.