In the United Kingdom, discussing the merits and effectiveness of nuclear deterrence has until now been somewhat taboo. Experts and the military respect the principle of "strategic ambiguity," which means giving an adversary as little information as possible about the possible use of nuclear fire to reinforce its deterrent potential.

For some weeks now, lips have been loosening as concern has grown over American commitment to Europe. Unlike France, which prides itself on its strategic autonomy, the UK, the only other European country with a nuclear deterrent, depends on a long-standing partnership with the United States. What would become of its deterrent if Washington were to cast doubt on or abruptly end this collaboration? Isn't it advisable to prepare for the worst, even if it is not at all certain?

At a House of Lords International Relations and Defense Committee hearing on March 5, former British ambassadors to the US made no secret of their concerns. Sir David Manning, ambassador to Washington from 2003 to 2007, said, "It is very difficult to imagine what we will do to defend ourselves if, for example – this is very hypothetical – the Trump administration decide that they will end our nuclear cooperation deal, or Trump moves out of NATO [North Atlantic Treaty Organization], or even becomes just so equivocal about NATO that the Article 5 guarantee [which states that armed aggression against one country in the Alliance should be considered an attack on all its members] is no longer plausible. I am not saying those things will happen. They were inconceivable just six weeks ago. Now we have to address them."

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