Why does He 177 have two nose gun positions?

[Johnny .45]

Thank you Juha; that was very educational. For some reason, I've had it in my mind that the gondola gun was remotely controlled. Not sure where I got that idea; probably something I read on line and took too literally. Anyway, now that I look at the cutaway drawing I have in my book here, I notice that the MG 151/20 is equipped with a gunsight and bullet-proof glass, which should have made it clear that it was manually operated!
By any chance does your manual mention which crew operated which guns? Was the bomb-aimer responsible for both upper and lower guns? Or was the navigator who fired the MG 81Z (or MG 131) in the rear of the gondola supposed to man both the front and rear gondola guns? That sounds like the more logical thing somehow.