Popular culture is chock-full of depictions of experiments performed on soldiers to enhance their performance and make them less vulnerable on the battlefield or otherwise. So-called "super soldiers" like Riley Finn in Buffy the Vampire Slayer or Captain America and Red Skull from the Marvel Universe, all represent the results of military experiments to create the perfect human or human hybrid. Injecting someone with a serum or drug to make them more powerful or trying to create a human with the abilities of a supernatural being might sound like something that only exists in comic books but it is something the US military has been trying to do for decades, in one way or another. Militaries have been attempting to create super soldiers to gain the strategic advantage for centuries, dating back to the Inca warriors in pre-modern times. The goal is to create a more effective, powerful, heroic force like you see in Captain America for example but to do so, you run the risk of creating something dangerous with serious and long-lasting implications like Red Skull.
Since the beginning of warfare, soldiers have been using drugs to enhance their military capabilities. Civil War soldiers used morphine and German soldiers in WWII used crystal meth, a habit encouraged to dehumanize soldiers, make it easier to kill, and even combat stress. The advancement of technology has changed this approach but with similar goals. Since 1990, DARPRA, the central research and development organization of the Department of Defense, turned its focus to creating a new kind of soldier. Exoskeletons are one example of that focus but there is also the push to go beyond that to lessen the effects of fear and fatigue on soldiers. During his time as Director of the Defense Science Office (DSO), a department within DARPA, Michael Goldblatt went as far as to hire a biotechnology firm to develop a vaccination that would reduce pain so soldiers could continue to fight regardless of injury. In a program called the Brain-Machine Interface, the DSO explored the possibly of brain implants to enhance cognitive ability and possibly lead to telekinesis.
There are several other experiments intended to enhance soldier performance that have been declassified and there are undoubtedly countless others that remain a secret. The effort to keep soldiers safer while making them more effective is an understandably salient project but is stripping them of their humanity the answer and where do you draw the line? Quite often, the knowledge of when something has gone too far is what separates a hero from a villain.