if it's useful, the british army were first deployed in ulster in august 1969, following the battle of the bogside in derry. the stormont government at the time requested their deployment on the 14th august.

my (late) father was in the ruc and we have family friends who he met while they were over on tours of duty in the early 70s, with either the royal lifeguards or the blues and royals (can't remember for definite which, but i'm pretty sure it's the former)