This is the whole sorry tale of the British Army and FRES that resulted in the rather heavy, but otherwise far from earth shattering Ajax.
It also has some interesting things to say about US 'medium weight' armour ideas and those of other nations.
Be warned it is a long read, starting from CVR(T) Scimitar going all the way along, the vastly expensive, track to Ajax...
http://www.thinkdefence.co.uk/from-s...-fres-to-ajax/