Bismark
A bit off topic (sorry) but...
It is a bit like the deployment rates for individuals. When I was serving one always used to see an RAF individual deployed for 4months and 2 days - why? The answer appeared to be that if he/she served for less than this then he/she would not be entitled to the Op Welfare package!
Everyone gets the op welfare package (apart from the mine hunter force in the ME), its the R'n'R bit you gain over 4 months. The RAF stopped doing 4 month and 2 day tours some time ago; you deploy for <4 months (and no R'n'R) or 6 months+. And I believe that we are all going to 6 months+ now anyway.