Gunner on military trucks..?

my husband is deployed in iraq right now. they were suppose to have him on radios, because he has a bad knee. they changed his section, he didn't want to tell me, but he's the gunner now. i really worried. the way he explains it looks like, i don't get it. can someone find me a picture just to get an idea. i don't even know what's its called. please :(