In addition, Ryan Crocker will be nominated to take over from Karl Eikenberry at ambassador to Afghanistan and General John Allen will assume command of ISAF in Kabul when Petraeus leaves.

There is a lot in these moves but one especially interesting detail is that when Petraeus takes over at Langley (his Senate confirmation is a virtual certainty) in early September, he will do so wearing a business suit and not his uniform.

Petraeus (who discussed the CIA job with President Barack Obama on March 14th and March 18th) will retire from the Army at the end of a storied 37-year career.

That means that despite being probably the finest military officer of his generation Petraeus will retire without having occupied either of the top two jobs available to him – Chief of Staff to the Army or Chairman of the Joint Chiefs of Staff.

It seems that the Obama administration did not seriously consider Petraeus as Chairman of the Joint Chiefs, the number one job in uniform. Obviously, becoming CIA director is hardly a demotion and it opens up all sorts of opportunities for Petraeus, not least an eventual run for the presidency. But it does seem curious that Petraeus was not in the mix to lead the US armed forces.