Thats true. Most of it is classified. I think the concepts are not classified. Like type of radars etc.
I found lot of pics of E3 here.
http://www.nme.de/cgi-shl/NME/viewcat.cfm?cat=21
Depending upon flight altitude hundreds of air can - with the rotary Westinghouse radar An/apy-1 in the Rotodom over the trunk, See-und ground targets to approximately 400 km distance to be supervised and pursued. Will conveyed the data at command centers at the soil, but can interceptors also from board be led.