Who is right on UK defence capability?
Prime Minister David Cameron has moved swiftly to counter the criticisms of the former US Defence Secretary Robert Gates, insisting that Britain is still "a first-class player" in defence terms with "the fourth-largest defence budget anywhere in the world".
Mr Gates had lamented that defence budget cuts in Britain had left it without "full spectrum" or across the board military capabilities. In the future, he argued, Britain wouldn't be able to be a full partner to the US as it has been in the past.
So who is right? Well of course they both are - they were not really talking in the same terms.
A quick and informal telephone poll of British defence experts prompted the consensus view that Mr Gates has a clear point. The former US defence secretary cited in particular the decision in the 2010 Strategic Defence and Security Review that left the UK without an operational aircraft carrier until the new Queen Elizabeth is ready for operations in 2020.
You could add to the list. No dedicated maritime reconnaissance capability; an insufficient number of sophisticated Unmanned Aerial Vehicles (UAV); the gradual withdrawal of Tornado squadrons - by 2020 the RAF will depend, in fast jet terms, upon its Typhoon force with the first of the new F-35 units only just becoming fully operational, and so on.Budget crisis
But as Mr Cameron notes Britain remains a major league defence player, certainly when compared to its European partners. He could have noted - perhaps he was too polite - that Mr Gates has also had to make some serious defence cuts of his own.
Britain's defence budget was in crisis when the coalition came to power. The wider economic situation dictated retrenchment and significant savings.
Four things matter to the US in the broad military relationship between London and Washington. Firstly Britain's nuclear deterrent; secondly the strategic partnership between the two countries' intelligence agencies; thirdly the professionalism of Britain's special forces; and finally the capabilities of Britain's conventional armed forces as a whole.
Barring a decision to renounce nuclear weapons, which does not seem likely, the first two elements of this relationship look in relatively good shape.
It is the second two that present potential problems. Cut-backs in troop numbers reduce the recruiting pool from which special forces can be drawn. A smaller army still means that Britain can take on important roles, but inevitably its ambitions have been scaled back.
For example, current plans are based on the ability to deploy an enduring stabilisation mission of some 6,500 men. Before the 2010 Defence Review the ball-park figure for such a deployment was some 10,000.Reduced ambition
It is this problem of matching ambition with available resources that is key. As Brig Ben Barry - the land warfare expert at the International Institute for Strategic Studies said - there is evidence of reduced ambition in many of the decisions that have been taken.
He noted the reduction in the number of heavy armoured and mechanised brigades, the reduction in size of the Navy's Commando Brigade and the Army's 16 Air Assault Brigade, the growing emphasis in key areas like logistics upon reservists and so on.
This all has a bearing on the speed with which forces can be deployed and indeed on the size of force that can be despatched in the first place.
Of course numbers and bits of kit matter. But there are other crucial factors at work too.
The Chief of the Defence Staff - Sir Nick Houghton - in his Christmas lecture last year to the Royal United Services Institute, made the point that over the last 20 years, western militaries in general had given too high a priority in preparing for conflicts against similar state-based actors.
This, he argued, resulted in investment in "exquisite technology" but not enough concern with manpower numbers and activity levels.
This was not, as some simplistic headlines put it at the time, the country's most senior military man just putting down a marker against future troop cuts. It was, with the withdrawal from Afghanistan and preparations for the next Strategic Defence Review in 2015, just beginning, a call to widen the debate.Strategic review
The list of factors that need to be encompassed in such a review goes way beyond the evidently important matter of available resources and the will of government to spend them on defence.
There are fundamental questions about the changing nature of armed conflict. There is still a debate as to what recent wars have actually achieved? What are the successes and what the failures?
How much public backing is there for the expansive use of military force as a policy too? There seemed to be a collective national sigh of relief when Parliament refused to back the use of force against Syria for example.
Are we still geared up as a nation for the risks of armed combat? Gen Houghton seemed to hint at his answer to this question when he referred to the French forces' ability to operate "with a mindset of aggressive risk management".
Many experts have to an extent written off the last Strategic and Defence Review of 2010 as essentially an exercise in budgetary discipline - a need to force defence spending into the constraints of a grim financial environment.
Money may not be plentiful, but the next review may perhaps be able to take a more "strategic" view.
Mr Gates' fears hint at one possible trajectory for Britain's armed forces. Smaller is smaller and there is no getting away from that. But wise choices; further steps to grapple with defence inflation; and genuinely strategic decisions about the nature of future threats and the means to counter them, should make Britain a valuable partner to Washington for the foreseeable future.