Britain and France are to set up a joint military force and share equipment and nuclear missile research centres in what Prime Minister David Cameron hailed as a new chapter in their relations.
Treaties signed by President Nicolas Sarkozy and Mr Cameron in London today will pave the way for an unprecedented degree of military cooperation between the two neighbours, western Europe's biggest defence spenders.
The Nato allies, and Europe's only nuclear powers, have a centuries-old history of military rivalry and, more recently, have differed sharply over issues such as the Iraq war.
Their new partnership is driven by the desire to maintain cutting-edge military capabilities while at the same time reducing defence spending to rein in big budget deficits.
The two countries have agreed to set up a joint brigade-sized army contingent with air and sea support, which could assemble as needed to take part in Nato, European Union, United Nations or bilateral operations.
"If we come together, and work together we can increase not just our joint capacity but crucially we can also increase our own individual sovereign capacity to make sure we are able to do more things alone, as well as together," Mr Cameron said.
France's Charles de Gaulle aircraft carrier and a British carrier that is just being built will be made compatible so that each country could fly their planes off the other's carrier.
The ultimate aim is for the two countries to coordinate so that one carrier is at sea at all times.
The deal comes two weeks after Mr Cameron's government announced it was cutting Britain's £36.9 billion defence budget by 8 per cent in real terms over the next four years to help rein in a record peacetime budget deficit.
Reuters