At a certain Tonka base in East Anglia in about 1987, we'd recently had our old radar replaced with a brand new on on a nice high tower. One sunny Saturday morning I'm pottering in the garden when I hear the roar of a pair of Merlins and look up just in time to see the BAe Mosquito above me, going like a bat out of hell, on it's way to a display. Commenting on this to an ATC colleague later on, he told me that the radar simply didn't pick it up until it was about a mile away and then lost it after only a few more seconds as it headed away.