Britain and France are being forced by budget cut-backs and the lack of their own strategic capability to cooperate more closely on defence.
They both want to be global players but increasingly lack the resources to remain so.
A series of measures are being formally agreed at a summit in London on Tuesday between Prime Minister David Cameron and President Nicolas Sarkozy.
The Chief of the British Defence Staff General Sir David Richards has said they will develop an "expeditionary joint force" in which there will be cooperation at brigade level "but not within the same brigade".
This will not be a standing force but will involve designating forces to take part in any joint operation. It will be at brigade level, that is about 5000 troops from each partner depending on the operation. There will be a joint political decision to deploy but one overall commander chosen for the operation at the time.
A lot of this is on the technical side because that is where cash can be saved. One new idea is to pool resources on the testing of nuclear warheads by technical means. Technology for this will be developed in Britain and testing will be done in France. The ability to test warheads this way is vital given the bans both governments observe on explosive testing. Each side will keep control of its own warheads.
They will share air-to-air refuelling because Britain might have spare capacity in this in the future. There is scope for joint maintenance work on transport aircraft, and shared development of a drone, mine-counter measures, satellite communications and cyber warfare.
There is a plan to allow each other's aircraft to use the one carrier they will each eventually have and to try to ensure that one partner always has a carrier at sea. This is an example of how money is driving this change. Neither can afford to have two carriers so have agreed on a sharing arrangement.
How some of this will work in practice also remains to be seen. Interoperability on carriers requires both countries to be committed to the same conflict for it to have any major practical use.
The French Defence Minister Herve Morin has already indicated that partners would "disengage" in "a conflict where our respective interests diverge". This is also how the concept is seen in London. Each side will have a veto on a deployment it does not want.
It is being stressed on the British side that all this is being done outside the European Union and is not designed to undermine Nato.
'No EU army'
The British Defence Secretary Dr Liam Fox said: "This is not a push for an EU army which we oppose... It has always been my view that defence must be a sovereign and therefore an inter-governmental issue."
Britain is therefore not taking advantage of the mechanism offered by the Lisbon Treaty. The treaty allows for what is called "permanent structured cooperation in defence".
This is in effect an EU "opt-in" arrangement. It allows member states to get approval from the European Council (the heads of state and government) to organise combat units capable of operating on missions up to at least 120 days.
Such EU-led cooperation was envisaged in 1998 when Tony Blair and President Chirac agreed at St Malo that "The [European] Union must have the capacity for autonomous action, backed up by credible military forces".
That has not happened. Instead, France has re-joined the military structures of Nato and, although the French would probably have wanted to go down the EU route this time, Britain is saying no and France is saying OK.
The question remains, though, as to whether in time this creeping co-operation might not lead to the "progressive framing of a common Union defence policy" agreed to in the Lisbon Treaty.
In the meantime Dr Fox declares that the new Franco-British defence relationship will be "the closest it has ever been".
This is debatable. It might be true in the sense of sharing facilities but hardly true in the sense of sharing commitments. Just think back to the First World War, when Marshal Foch ended up by commanding all French and British armies and a respectful Britain put up a statue of him outside Victoria Station.
And before that there was a secret military arrangement, simply called "conversations", which shows how what starts out as a theoretical contingency plan can develop into a major commitment.
The British cabinet as a whole was not told but the military staffs were given permission to develop plans under which Britain would come to France's help in the event of a German attack.
The talks were formalised in 1912 in an agreement to divide naval forces - if there was a war and if Britain joined in, Britain would take care of the Channel and France the Mediterranean.
Even though the British government kept on stressing that the plans did not commit it to a war in support of France, the practical and moral basis was being developed upon which Britain did commit itself to France and to a war with Germany.