Someone must know.....
....and I suspect it might be whoever pays our pensions. In 1965 the average length of time for a full career officer retiring at 55 to draw his pension was - THREE YEARS!!!
My just about to be my F-i-L showed me those figures from the (as it was then)
Officers' Pension Society.
At one of my resettlement financial seminars in about 1996/7 I asked the question again but no-one seemed to know the answer.
The Ancient Mariner
(F-i-L lived to 91,chuffed to bits that he'd beaten the actuarial odds)