The Vatican comes with its ills, contradictions and blatant hypocrisies in the field of moral theology and human existence, but on the issue of atomic and nuclear weapons, the position has been fairly consistent, if marked by gradual evolution. On February 8, 1948, Pope Pius XII held an audience with members of the Pontifical Academy of Sciences. “What misfortunes,” he asked, “should humanity expect from a future conflict, if it should prove impossible to arrest or curb the use of ever newer and more surprising scientific inventions?”

The Second Vatican Council through its 1965 document Gaudium et spes deemed the arms race “one of the greatest curses on humanity and the harm it inflicts on the poor is more than can be endured.” Using nuclear weapons exceeded “the limits of legitimate self-defence”, and would constitute a “crime against God and against humanity itself. It merits unequivocal and unhesitating condemnation.” Pope Paul VI would subsequently give his approval to the Nuclear Arms Non-Proliferation Treaty, making nuclear disarmament a matter of highest moral urgency.

But attitudes to nuclear weapons were always chained to the Cold War orbit and the old dilemmas of self-defence. In November 1980, with the election of US President Ronald Reagan, Auxiliary Bishop Thomas Gumbleton of Detroit expressed genuine terror at the prospect of a pro-bomb enthusiast in the White House. “We’ve just elected a President who has stated his conviction that we can have superiority in nuclear weapons, an utter impossibility. We have a Vice-President who has clearly stated that one side could win a nuclear war and that we must be prepared to fight one and to win it.” But the concern on the part of US bishops, expressed through The Challenge of Peace: God’s Promise and Our Response, was influenced by an admixture of interference and moderation on the part of The Vatican.

Pope John Paul II was keen to keep things cordial with Reagan, preferring revisions to be made to the original drafts of the pastoral. While the pontiff kept up public relations appearances by visiting Hiroshima and meeting with the Hikabusha, the mutilated and maimed survivors of the world’s first atomic blast, he was also mindful of the big power game and Reagan’s initial hard line against the Soviet Union.

The Catholic Church was also at odds in how best to reconcile dealing with nuclear weapons, given the Cold War language of evil so heartily promoted by Reagan, with its multi-barbed opposition to godless communism. The US-Soviet struggle, moralised Reagan at the Annual Convention of the National Association of Evangelicals in Orlando, Florida was nothing less than a fight “between right and wrong and good and evil.” The final text of The Challenge of Peace affirmed the Catholic view that a sovereign state might well engage in self-defence, but that could only ever happen in accordance with the limits of just-war theory.

The current pontiff Pope Francis has layered his comments in line with a growing body of thought suggesting that the use of nuclear weapons in any circumstances, including their possession, would be illegal. Nuclear boffins see him as “unusually active compared to his predecessors in nuclear diplomacy.”

To use such weapons, he reasoned in his November 2017 address to the symposium “Prospects for a World Free of Nuclear Weapons and for Integral Disarmament” would result in “catastrophic humanitarian and environmental effects.” Having such weapons encouraged a fallacious, dangerous logic. They were tactically futile, wasteful and could be used by mistake.

Pope Francis also noted the moves by the United Nations to draft a binding instrument that would prohibit the use of nuclear weapons, resulting in the Treaty on the Prohibition of Nuclear Weapons. Through a conference in 2017, the General Assembly voted to adopt the Treaty by a vote of 122, with one abstention, and one against. (A truly “historic” vote, claimed the pontiff, one that “filled a significant judicial lacuna”).

The text considers “that any use of nuclear weapons would be contrary to the rules of international law applicable in armed conflict, in particular the principles and rules of international humanitarian law.” Outlined prohibitions include undertakings never to, “Develop, test, produce, manufacture, otherwise acquire, possess or stockpile nuclear weapons or other nuclear explosive devices”.

Such views align with the long held view of the International Campaign to Abolish Nuclear Weapons (ICAN), though not those of the International Court of Justice, which maintains the position that the use of nuclear weapons may be permissible in “extreme circumstances of self-defence.” In the aftermath of the group being awarded the Nobel Peace Prize, ICAN Executive Director Beatrice Finn reiterated the position that, “Nuclear weapons are illegal. Threatening to use nuclear weapons is illegal. Having nuclear weapons, possessing nuclear weapons, developing nuclear weapons is illegal, and they need to stop.”

As with John Paul II, Pope Francis made a trip to Japan to reiterate his position. In Nagasaki’s Atomic Bomb Hypocentre Park, he dismissed nuclear deterrence as viable, claiming that peace was inconsistent with the “fear of mutual destruction or the threat of total annihilation.” Nuclear weapon stockpiles were symbols of squandered wealth even as “millions of children and families live in inhumane conditions.” Before a gathering at Hiroshima’s Peace Memorial Park, he spoke of the annihilation of “so many men and women, so many dreams and hopes” in the aftermath of the “incandescent burst of lightning and fire.”

Whatever reservations critics and observers might have of The Vatican and its foreign policy, the current pontiff’s concerns should be filed along those of other states agog before what looks like a spike of interest in military experimentation. The Intermediate-Range Nuclear Forces Treaty has been canned by the Trump administration; the Russian response, after initial indignation, has been one of resigned adaptation. The stalled denuclearisation issue over the Korean Peninsula is likewise something setting regional powers on edge. But the efforts to deem the very possession of such weapons of indiscriminate mass murder illegal continue their inexorable momentum.