Concrete base pads for TTR (Target Tracking Radar) and TRR (Target Recognition Radar). Also, according to Peter Snowberg, TRR also stands for Target Ranging Radar: "Improved Herc system added a third tracking RADAR that was dedicated to range info (Target Ranging Radar) which was [only] 60 kW and had two tunable magnetrons for quickly changing frequencies. The TRR was for ECM (electronic counter measures), insurance against jamming."