A Hampden bomber from 49 Squadron RAF crashed into the hillside on the night of March 21, 1941. The four man crew were killed. The stone bears an incised cross under which has been inscribed:
R D W
C J L
R L A E
The above represents the squadron number (49), the initials of the crewmen and the date of the crash. In 1991, the Aircrew Association rededicated the stone and added a commemorative plaque on the revers that recorded the date of the crash as 22nd March.
The crew members were Pilot Officer The Honourable Robert Wilson, Sgt Robert Brames (Wireless Operator/Air Gunner), Sgt Richard Ellis (2nd Pilot) and Sgt Charles Lyon (Air Gunner). Evident the pilot survived until the next day - it is thought because he was found still strapped in his seat. A really useful website provides much information about the memorial HERE - scroll down to the links for the crew names. These lead to photographs of the graves.
Here is a more recent photograph, showing the plaque, taken by Roger Cornfoot (Creative Commons).
Curiously, not far away, I saw the remnants of anti-invasion measure from the Second World War. Pine poles were erected all over Hamel Down early in the war to obstruct a glider-borne invasion. Here is a photograph taken by Mike White (Creative Commons) which shows one of the poles still standing. I remember being intrigued at the way the knots protruded as the outer layers of wood were eroded by the elements.