Yes, one essay that answers both. And word of advice: keep your essay in the word limit. Nothing upsets admissions more than students who don't follow word limits, and worse, submit super long essays.
I just had to reply here ... I've seen some of this negative behavior, but thankfully not too much of it. I think most of Annapolis loves the Academy and understands what comes with it.
That said, I know of a faculty member at the USNA who is actually trying to combat some of this...
I think the laptop issued to the class of 2015 (which was linked above) was new this year, so I wouldn't be surprised if 2016 gets the same thing.
I don't really know for sure, though!