P-40E Warhawk: What is that black circle inside the starboard rear vision window?

[MrSmoothie]

Visible in most photos of the P-40E is small circle, starboard side only, just forward of the first vertical strap. The photo of the USAF Museum's example shows it clearly, as well as the cutaway drawing. Most modern "walkaround" photo essays don't show it because the canopy is slid bark.

Is this an object or an opening? If I didn't know better, I'd say it was a small speaker. If so, what would have been the purpose?

Does anybody know for sure?

 

[MrSmoothie]

Aha, just heard from somebody. It was a speaker -- "landing gear horn". Mystery solved.

 

[72modeler]

I think you meant portside for the circular device, as seen in the posted photo? If so, it appears to be a E-2 warning horn used when the throttle was retarded and the landing gear was still up. See the photo.
Mike