We now have a deadline for the UK to spend 2.5% of national income on defence and it’s much sooner than anyone expected.  But cash doesn’t just turn into military might.

There are many things you could spend it on. People? Hardware? Training? The real question is what you should spend it on, for the right capabilities at the right times.

There are urgent priorities to rapidly improve defence of our own doorstep as the US pulls back, but we still need to plan for long term battle-winning edge.

Professor Michael Clarke explains why ‘invisible’ capabilities will be favoured over heavy metal, while Matthew Savill from RUSI assesses how hard it will be to deliver the Defence Secretary’s priority of “arresting the long-term fall in numbers of service personnel”.