In Star Trek Into Darkness, Admiral Marcus puts Khan to work for him, on projects designed to enhance the military capability of Starfleet.
For instance, Khan is a principal consultant on the construction the USS Vengeance and is intimately familiar with its design.
Why does Marcus need Khan's assistance, and how is Khan even able to give this assistance?
Khan may have a superior, generically-engineered intellect, but he is not a starship designer, he's not a phaser specialist, he's not a warp field mechanic, and so on. He is a man from the 20th Century. A cunning man, for certain. Able to outwit an opponent? Often (but not always). But I don't see how he can be so essential to Marcus' plans, which rely very much on the development of technologies fit for the 23rd Century. I realize that Khan was a quick study in TOS "Space Seed". But still.
Why would Marcus need Khan's work on Vengeance? Surely, starship designers of the time would simply listen to Marcus' requests and then follow orders to build a bigger, faster, more powerful, and more menacing ship.
I can understand if Marcus would want Khan's advice on how to manipulate the situation with the Klingons, using his experience as a one-time fairly successful despot on Earth. But starship design? Even if Khan were able to provide input, surely there are already experts working for Starfleet and Section 31 in the 23rd Century that have the know-how to realize Marcus' vision when it comes to Starfleet hardware.
Khan doesn't really have a monopoly on "savagery" (Marcus has enough of his own), and all Marcus needs are personnel and engineers that can follow orders, and making a menacing starship does not really require an evil genius. So of what actual use is Khan to Marcus, and how is it that Khan is able to provide such technical services?