[ Gaunt notices the pause and acknowledges it with a raised eyebrow. ]
It depends on the method of enhancement. There are a great deal of Skitarii created by the Adeptus Mechanicus. Legions of them, in fact, though they mostly are garrisoning forge worlds or guarding explorator teams. There are imperial guardsmen who receive augmetic implants due to wounds, like myself, or voluntarily, though this is much rarer.
[ Gaunt frowns a moment as he continues discussing the various types. ] The Skitarii are barely human, in all honesty. More like servitors than men, they'll often speak only binaric and have entire limbs replaced with weapons like hellguns. Often they are also quite feral. The Machine Cult is very mysterious, and I know little of them beyond that, they don't share their secrets with the Imperial Guard.
Space Marines are also cybernetically augmented as well, to the point of more or less becoming transhuman. They are giants, angels, our protectors among the stars. There are less than a million of them to protect the endless population of the Imperium of man and still they are enough.