rlsbutler - thanks for that info. I am still a little confused - you describe OP as an active radar but also make it sound like an RWR (ie a receiver) when you say 'It gave a coarse quadrant display of a threat'. I could understand if the bombers were fitted with rudimentary RWRs to pick up AI radar equipped fighters (Jav/vixen in your time?) but not an active sensor. Can anyone enlighten me further?