For us they decided to make it extra fun and not allow us to use NODs. Also could have been they didn't want them broken/lost/getting caught on the wire obstacles. Either way, made it less pleasant. Make yourself as small a target as possible. Cover and concealment is not a guarantee. You aren't always going to move through a wooded area with trees, brush, and elevation cuts to hide you from enemy fire. So the next best thing is to drop to your stomach and slither like a snake. The low crawl is so low you are often literally dragging your helmet along the dirt.