to as short as 5 miles if it was under trees or otherwise blocked. SOE stated that they could be reasonably certain to place it on open ground. However, they also stated that they could only navigate to perhaps ten miles of the beacon, which would be only marginally satisfactory. Brown asked why they could not use the Gee navigation system to address this, and when they admitted they had no idea what this was, he had the satisfaction of saying he could not explain it to them because it was secret. Ultimately, Brown was taken to meet the C-in-C of the SOE and arranged a demonstration similar to the one given earlier for the Army. SOE was given the transponder and told to hide it anywhere within a large area, and their aircraft would not attempt to find it until a week later. On 11 February 1942 one of the TRE's Avro Ansons took off from RAF Hurn and picked it up at a range of , approaching and dropping two containers within 200 yards. An order was placed immediately. Prototypes One of the major problems with the original AI radars was that the transmissions spread out over the entire front hemisphere of the aircraft. Shorter wavelengths, like those used in AI, tended to scatter from the ground, sending a portion of the signal back towards the aircraft, the "ground reflection" or "ground return". For the simple reason that the ground is much larger than a target aircraft, the scattered signal overwhelmed any target return, and made it impossible to see any target further away than the aircraft's current altitude. For the supply mission, which was carried out at very low altitudes, this was clearly not going to work. As the SOE had their own aircraft, and there was no need to make the system work with an existing production radar design, the solution was relatively simple. Instead of the transponder replying on the same frequency, and thus being lost in the ground reflections, it would receive the signal from the radar and then re-broadcast it on a second frequency. In the aircraft, the receiver would be tuned not to the radar's broadcasts, but the transponder's. This way the ground reflection would simply be ignored, although at the cost of requiring the transponder to have two separate antenna systems. Powering the transponder was a more serious problem. The system