This area of heath has many bomb craters, reminders that the area was part of the Ashley Walk test-bombing range during the Second World War. There is a large crater at
SU199142, left by the "Grand Slam" test bomb which missed its reinforced concrete target by a short distance. The bomb, the largest conventional weapon ever deployed, was quite remarkable for its engineering, and impact - see
the Grand Slam article on wikipedia for more. The 130-foot crater in this grid square was left by the 10-tonne bomb which was released high over Sandy Balls, broke the sound barrier as it fell and buried itself deep in the ground before exploding. The history of the range is briefly discussed
here and in detail in the booklet "Ashley Walk: its Bombing Range, Landscape and History" by Anthony Pasmore and Norman Parker.