Student or Learner
He'd manned a machine-gun nest to hold back the North Vietnamese.
Does it mean he took over the position where the machine guns were placed and using them stopped the Vietnamese soldiers?
I would say that he manned a machine gun. (A "nest" might be more than one.)
I have a feeling that 'nest' refers to the ring of sandbags that protects the machine-gunner(s). But it's not something I have strong views about either way
In a machine gun nest there are normally at least two people--one to fire the machine gun and another to feed it ammunition.