What is the name of the movie with the soldiers going crazy from their new equipment?

I watched this movie about 10 years ago, and was really scared by it
(i was still young). Now, i want to watch it again, but i can't seem
to find it anywhere.
The plot was a bit like:
Soldiers going for a mission in some desert'ish country. They have
received some new equipment that they need to test out. It turns out
that that equipment is drugging them or something, turning them crazy,
making them see things they don't really see.
I remember one scene where you see a little boy holding a handgrenade,
then showing the pin, then exploding. But later you see what really
happens: a soldiers holds a grenade in his own hand, comitting
suicide.
Also, another scene i remember, is when one of the soldiers goes in
some underground building, where he finds a buddy of his, with some
surgeons around him, cutting away on his body.
If this rings any bell, please say so :)