Pope Francis has condemned not only the use but also the possession of nuclear weapons, and the Holy See was one of the first countries to sign the international treaty that will make their possession illegal. A US-based theologian makes the moral case against nuclear deterrence

August witnessed the 75th anniversary of the destruction of Hiroshima and Nagasaki. Last week, an important threshold was reached when the 50th country ratified the UN Treaty on the Prohibition of Nuclear Weapons (TPNW) which will bring it into force on 22 January. Archbishop Paul Gallagher, the Vatican’s foreign minister, signed it on behalf of the Holy See in September 2017.

But the world’s nuclear-armed nations show little inclination to sign. Earlier this year, the UK Defence Secretary announced a nuclear warhead replacement programme. For the US Department of Defence, nuclear deterrence remains its “#1 priority mission”. Both countries are members of NATO, which makes it clear that, should the fundamental security of any of its members be threatened, it has the capabilities, both nuclear and conventional, to impose costs that would “far outweigh” the benefits that any adversary could hope to achieve.

Defenders of nuclear deterrence urge that the threat of mutually assured destruction (“MAD”) has prevented war between the major powers since Hiroshima. The Church’s position has been widely understood to be that nuclear deterrence can be moral if part of a process leading to multilateral disarmament. This was the position taken by the US bishops in their 1983 Pastoral Letter The Challenge of Peace. They quoted Pope John Paul II’s words to the UN the previous year: “In current conditions ‘deterrence’ based on balance, certainly not as an end in itself but as a step on the way toward a progressive disarmament, may still be judged morally acceptable. Nonetheless, in order to ensure peace, it is indispensable not to be satisfied with this minimum, which is always susceptible to the real danger of explosion.”