Originally Posted by
Dan Winterland
The Germans also homed onto H2S (ground mapping radar), the IFF and Monica (rear radar). The always knew when the bomber streams were coming and in some cases could locate individual aircraft. It wasn't fully appreciated by the RAF despite warnings form the scientists. R V Jones' excellent book, Most Secret War' covers this in detail.
I think it was known, but squadrons didn't always mention it. It was standard practice in 5 Group to keep IFF on even up to 1942, in the belief it jammed German radar. IFF would never normally be activated once they climbed to height, until they made near to landfall back. Monica was withdrawn in summer 44, after the capture of a German nightfighter.