pour info :
Exercise Purple Warrior was a British military exercise conducted in south west Scotland in November, 1987.
This exercise was designed to test lessons learned during the Falklands War.
as far as i know, operation Purple Warrior was undertaken in november of 1987, as a test of the lessons learnt during the Falklands war, i cannot find the exact details of the units that were part of the exercise, but the British SAS were used in this as they were the first ones to be sent in at the start of hostilities during the war. Perhaps your father was part of the regiment. Not many details of this exercise are available as it is still considered secret.
voir détail:
http://www.merchantnavyofficers.com/purwar.html