AP Photo

In times of trouble, it is always reassuring to think that we can count on Washington's support to get us out of a fix. OK, so the Americans have an irritating habit of turning up late, and then claiming all the glory, as was the case in the two world wars. But even today, in the killing fields of southern Afghanistan, the arrival of 30,000 US Marines three years after British troops first deployed to the region has immeasurably improved our chances of defeating the Taliban, as I discovered during my visit to Camp Bastion last week.

It is mainly to guarantee American support for our freedoms that, alone among the major European powers, Britain has little hesitation in signing up to fight America's wars. In the past decade, more than 500 of our personnel have sacrificed their...