.. when did you join up?
If you joined after 6 April 2005 you will be a member of the Armed Forces Pension Scheme 2005 (AFPS 05). If you joined between 1975 and 5 April 2005 you will be a member of the Armed Forces Pension Scheme 1975 (AFPS 75). If you are/were in ''75'', you will have been offered the chance to switch and make a deliberate decision to join ''05'', and could remember it.