US Technical Intelligence Reports
 

Whilst I have come across several of the A-prefixed reports in my researches and have a decent collection of these, I have only come across a small number of those prefixed E, I and N. I've always assumed A stood for aircraft or airfield. Does anyone know better on this point?

Those prefixed I are obviously Interrogations of which I've seen a couple. I've seen one each of those prefixed E and N and I'd welcome clarification of the purposes of these.

Equally, are any decent archived holdings of any of these three types of reports available and can anyone point me in the right direction ?