As a general rule, we should all encourage and support international cooperation. Once in a while, however, a proposal comes along that is so disconnected from reality that you check the date in case it’s April Fool’s Day. There is now such a proposal on the table.

The French government has suggested that France and Britain pool their ballistic missile-firing submarines — ‘boomers’ — in effect merging their nuclear deterrent forces. This would allow some savings on operational costs, since at the moment each country always has at least one boomer at sea. Under the French proposal, they could just keep one submarine at sea, hidden and invulnerable in the mid-ocean depths, ready to retaliate against an attack on either Britain or France.

The whole policy of always having one boomer at sea is a left-over from a different era anyway. During the Cold War, when countries worried about the other side launching a nuclear Pearl Harbour, it made sense never to have all your missile-firing subs in port where they could easily be destroyed. It’s the classic logic of deterrence. If the other side knows for certain that at least one submarine will survive, and shoot back with dozens of unstoppable nuclear warheads, then it won’t attack in the first place. That’s why Britain has four “Vanguard” class boomers and France has three “Triomphant” class boats with a fourth building: so there will always be one at sea.

But if Britain and France insist on maintaining these patrols, then they have to realize that one submarine cannot provide cover for both countries. The idea was apparently discussed for the first time when President Nicolas Sarkozy visited Prime Minister Gordon Brown in London in March 2008, but it’s not likely that either man really understands the theory of deterrence. So here, for their benefit, is a potted version of the strategy.

Poor combination

Let’s suppose that it’s a British submarine out on patrol, and some evil country strikes France with nuclear weapons, eliminating all of France’s boomers in port. Does the British submarine retaliate with its own nuclear weapons, knowing that to do so means that Britain may also be attacked by nuclear weapons?

If I were French, I wouldn’t trust British promises about this. And if I were running the evil country in question, I would likewise doubt that Britain would really retaliate against me on France’s behalf, knowing that I might then hit British cities too. In practice, when Britain has to choose between its loyalty to the European Union and its instinct to go with the United States of America, it almost always chooses the latter option. France has always had less faith in American judgment and in the US’s willingness to fight a nuclear war on Europe’s behalf, which is why it spent all that money over two generations to build a truly independent nuclear deterrent force.

The British nuclear deterrent force is different, since the missiles it uses have been American ever since 1962. There is no formal US veto over the use of the missiles that are in British submarines, but those missiles are only leased by Britain and belong to a pool of missiles that also supplies American boomers. A missile that is in a British submarine could be in an American one in its next service cycle.

The French navy must be furious at Sarkozy for offering to combine their genuinely independent nuclear force with a British deterrent force that is very closely tied to the US. Fortunately for France, the British navy doesn’t like the idea of job-sharing either, and can be counted on to resist, undermine, and ultimately kill the idea. The astonishing thing is that it ever got out into the public domain at all.