A historical turning point for France and Britain?
Britain and France have tried a few times in the past decade to cooperate more fruitfully on defence.
At times it's seemed to be going well but at others the US gravitational pull - irresistibly attractive to the British and repellent to the likes of former French president Jacques Chirac - have brought it to grief.
My own experience with troops from the two nations in the Balkans or Afghanistan suggests that British and French get on very well together.
They are business-like, often share a sense of humour and the French in particular have made great efforts to overcome the language barrier. Watching soldiers from the two nations dealing with Serb fire on Mount Igman in 1995 or training Afghan soldiers in Camp Shorabak earlier this year, you certainly wonder why commentators or tabloids bother trotting out their John Bull nonsense about Waterloo or Trafalgar on a day like today.
The answer, of course, lies with politics - and it is why the 'can it work' questions are not yet redundant even if they are best framed with reference to the recent past rather than to the days of men in bicorne hats.
Some of the clauses in today's agreement carry forward cooperation in practical areas where it will obviously be mutually beneficial. The two nations are going to pool resources on their tactical air transport fleets, as both countries introduce the new A400 aircraft into service. It will be the RAF's Hercules replacement.
If it's done smartly, joint training and support of an airlift force can save money and survive any political chills. After all, decades have passed since Britain and France produced military aircraft like the Jaguar, Puma or Gazelle together.
However, the new agreement extends cooperation into some new areas: joint scientific programmes to maintain the two countries nuclear weapon stockpiles; running aircraft carrier operations jointly; or jointly fielding a large expeditionary military force.
The 'would a French carrier take our planes to war with Iraq?' question is a perfectly legitimate one, though the two nations hope it would not materialise 75% of the time.
Each country wants to have one carrier with its own aircraft - it's only during refits that one nation could become dependent upon the other.
The really unprecedented area touched upon today is that of nuclear weapons cooperation. UK/US nuclear cooperation was central to the birth of the special relationship - and many at Aldermaston would argue that it's still vital.
But the new British coalition government has shown unmistakeable signs (for example in reducing the planned warhead load for the Trident replacement submarine) that while it loves the political status of having the bomb, it thinks it can cut the bill.
Now the UK and France are seeking to cooperate on nuclear 'stewardship' issues, establishing joint scientific teams and sharing data. This involves sharing information about the construction, maintenance, and development of warheads (much of which in the UK's case has been learned alongside the Americans).
This is undoubtedly new territory and it touches on the intimate secrets of a nuclear weapons power. Since the actual use of such weapons is so unlikely, this is a political matter above all.
The real question in the coming years will be whether the Cameron and Sarkozy governments signed this treaty at an unusual and short lived moment of political harmony - with the British sore about being too close militarily to the Americans and the French under an unusually pro-Anglo Saxon president - or whether they managed to exploit a historical turning point in which rivalries became irrelevant.