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OK, thanks Biggus thats clear now. Still a shocking indictment of our planing system "
Not really, every military in the world uses a similar system. Fundamentally you can only operate roughly one third of your force operationally at any one time short of the 'maximum effort'. The moment you do that, you then spend several years in most cases recovering.
One reason why SDSR makes so much sense in using 2020 as a planning date is because the armed forces and their equipment are so broken from years of back to back HERRICKs that 2020 is the earliest that the planning / training / maintenance cycles will be realigned to where they should be. The Forces have made clear that they need about 5 years to rebuild post HERRICK and get ready to go again. Thats one political reason why losing harrier became a lot more palatable - the planning assumptions are that outside of the odd 'bashing the natives with sharp fruit as we get our boys out' type extraction, we won't be doing any real tasks in that period beyond normal jogging. Why do you think the future amphib force is only configured to deliver 1800 pax - because thats what you need for an extraction mission.