When the requirement was originally written erm and agreed in nineteen eighty seven  all of the nations decided that erm we required a short take off and landing capability and that was based on the  sort of the then cold war situation where the prospects of  runways and airfields being very severely damaged in a sort of central European type of scenario, and therefore the possibility that there might be only very small operating strips available from those runways and that was the basis for the particular length that was decided at the time.