Coming into this late...

Bronx...my son just turned 11 he also tends to get fixated on "tasks" in game play. If he isn't putting Lego sets together he will get out his army men and have wars.
Scary...What I didn't realize while he was setting his stage he was also researching the different wars that occurred throughout time.
He took it a step further and dove into a historical atlas and memorized all the different nations and battles they had to become nations. This included cultures and Religions.

It might surprise you...your son may have an agenda in his play. These children think so outside the norm.
Have you asked him what he is doing ? He may have an actual strategy in his play.

I know my son will mumble and look the other way now when he knows he isn't talking or acting like a normal 11 y/o. I have to constantly tell him "son, please don't rush, talk clear and look at me...I WANT to hear what you have to say" Breaks my heart (hence my screen name).

My son started with WWII interest...It spiraled from there and it was all self taught. Maybe try getting a book on the "battles of WWII" and just give it to him. He may just want to know more
and thus school will begin.

My son taught world religions for his teacher last week. She was confusing students and DS took out a book he had and explained the differences in religions in different areas if the world. She thought I taught him...yea like I can teach him anything...LOL again this all started with little green army men on my kitchen counters.

My son will pick up on people getting frustrated with him and will instantly dummy or shut down. DS always asks me if I'm OK with what he is doing (he knows playing with little green army men is really for younger kids). I tell him carry on...
our secret <3. He is also very sensitive so I try really hard to listen which really isn't easy.

My son used to sneak his passion of the "moment" when I pay too much attention to it. Now I just breath and look the other way.

I am just starting my HS journey, I am sure I will have similar issues. Let us know how you all are doing...