John Ashworth Ratcliffe 'JAR' or 'Jack' completed his undergraduate degree at Cambridge University in 1924.  He subsequently carried out research into radio wave propagation at the Cavendish Laboratory, Cambridge.

Jack Ratcliffe was one of the senior researchers from the Cavendish Laboratories who joined the radar team.  After the sinking of a battleship in Scapa Flow in Scotland, he went to the Bawdsey Research Station with John Cockroft (and others) to put together a Coastal Defence radar intended to detect ships and surfaced submarines which they then installed on a suitable site at Scapa Flow.  When it was working, it also detected low flying aircraft at a range of 70 miles.  This was the genesis of the Chain Home Low (CHL) stations which were developed to supplement Chain Home with better detection of low flying aircraft.

He went on to set up the radar and electronics training for the RAF at Forres School in Swanage, and similar training for the Army at Petersham.  

After the war he returned to Cambridge where he lead the radio group at the Cavendish Laboratories.  From 1960 to 1966 he was Director of the Radio & Space Research Station at Slough.

John Ashworth 'JAR' or 'Jack' Ratcliffe CB FRS
12 December 1902 – 25 October 1987