What is the purpose of the box between the engines of an A-10? There is a curious box between the engines of an A-10. It's seems rather rudimentary, like an afterthought, although it was present on the prototype.

I've found a few cutaways but this part is hidden. I'm fairly sure that at least the front is hollow, so perhaps related to an APU. The question is, what is it for, and why, even in the context of the somewhat inelegant A-10, why so unrefined?


source: savasucakalari
It is the intake/exhaust duct of the cooling system.

Basically, the front side consists of the ram air duct, which feeds air into the ECU precooler, with the (heated) exhaust air vented out through the rear. The image below shows a closeup of the duct.



Image description: Kenneth Thompson, 576th Aerospace Maintenance and Regeneration Squadron aircraft mechanic, aligns a portion of the pre-cooler ram air duct onto the top of an A-10A Thunderbolt on Davis-Monthan Air Force Base, Ariz., Jan. 23, 2013. Source: warthognews.blogspot.in

Here's another image that shows a cross-section of the system. The cooling system (without the box) could be seen above the APU.



Image from pintrest.