If I may add my two pennorth to the 'job for life' discussion.
I joined as an apprentice stacker and the terms of service offered before I took HM's shilling were either 9 years plus three in the reserve or a straight 12 stretch for which I would receive the princely sum of £250 on completion.
However, after sucessfully escaping from Hereford as a fully-sledged SAC, I was offered service to age 55, which I declined at the time. Later on, I decided to go for the age 55 option but that was because domestic distractions other than darts, beer and having a good time laid greater claim on my financial resources.
GasFitter will view that as support for his comment that people are only in it for the pension. I looked at it another way: I enjoyed what I was doing.