In the Vietnam era the cockpit glass of the Hueys was just plain old plexiglass, good for stopping a bb gun and no more than that. Some pilots did have armor plates under their seats and in the door panels, but it still remained a dangerous job and a lot of pilots were killed by simple AK fire. To get a better perspective on the chopper war in Vietnam read the book "Chickenhawk" or the book "Firebirds". Both are excellent and very informative on this subject.