Blue Joker AEW Choppers and Blimps

Guy Hartcup, The Silent Revolution, Brassey’s,1993,P.230:
“UK Ground Early Warning Systems: (1953) In the days before over-the-horizon radar the answer (to a serious gap…aircraft incoming at altitudes of 500′-5000′) seemed to lie either in radars suspended from balloons flying at a great height or in radars mounted in small ram jet helicopters…US was working on the same problem…balloon-supported radars seemed to be the more acceptable proposal. (One) at 5,000′ would give a horizon range of 84miles. Blue Joker, as the scheme was called, would give sufficient time for (MBF) to scramble and Blue Streak to be counted down to 30sec. readiness. But before Blue Joker could be realised in the late 1950s, the threat of low-level attack had diminished.”
I learn something new every day.