AI (airborne intercept) and ASV (anti-surface vessel) radars developed in 1939. These were in use and upgraded until 1945.
There's a bit of history here:
http://www.pyetelecomhistory.org/pro...ms_1939_-_1946
and more info here under Airforce/RAF&RCAF/airborne search & gunlaying
http://www.qsl.net/pe1ngz/signalscollection.html