A century ago, the world witnessed the first use of weapons of mass destruction. On April 22, 1915, the German High Command launched their first chlorine attack with a bombardment of the trenches on the Western Front, sending a thick yellow cloud floating towards the French and Canadian lines. Its effects were horrific even by the standards of the trenches. Chlorine burnt the throat and destroyed the lining of the lungs. Many drowned in their own bodily fluids.

Two weeks later, the RMS Lusitania, a luxury civilian cruise liner, was torpedoed by a German submarine a few miles off the southern coast of Ireland, sinking it within 20 minutes. Almost 2,000 civilians died, including 128 Americans. The sinking caused a storm of protest.

Then, on May 31, the first aerial bomb attack took place on the city of London when a zeppelin airship dropped incendiary bombs, which rained down on the people of east London. The raid lasted just half an hour and the casualty list was slight. But the psychological damage and the sense of terror and insecurity it generated was incalculable. The horrors of Guernica in the Spanish Civil War were to come 22 years later.

These three innovations in mass destruction during those six weeks of April and May 1915 represented a watershed in the history of warfare and changed its face forever. They were the first to challenge the existing consensus about the morality and limits of total warfare. No technology since then has been considered too indiscriminate to deploy. From then on a single attacker could launch a weapon that could kill thousands.

These innovations were partly the result of technical expertise, as well as a reflection of German desperation in 1915 as the Western Front turned into a quagmire and Britain’s naval blockade took hold. Indeed, since the blockade deliberately targeted the German home front, and was designed to starve the German people into surrender, the blockade itself might be seen as a weapon of mass destruction. As always in war, the moral picture is a muddy one.

To its architects, gas was a battle-winning weapon that would break the stalemate and hand victory to Germany. In reality, it changed nothing. The French and British allies promptly experimented with their own gas weapons. These proved similarly difficult to deploy and sometimes calamitous – with clouds of gas being blown back towards their own side.

The use of chemical weapons during the Great War led to 100,000 battle fatalities and many more civilian casualties. Many instinctively recoiled from what seemed an inhuman weapon. Even the German officer who supervised the first gas attack at Ypres in 1915 wrote: “The task of poisoning the enemy as if they were rats went against the grain with me”. However, he added: “War is self-defence and knows no law. That will always be so as long as war exists.”

It is clear with hindsight that these three innovations a century ago were more or less counter-productive. The Germans’ gas attacks provoked allied reprisals. The U-boats, which were meant to starve Britain into submission by destroying its Atlantic trade, drew America into the war. Even the air raids over London only stiffened the resolve of civilians to see the war through.

It is salutary to remind ourselves about the consequences flowing from the first use of weapons of mass destruction

The four years of the war proved that the veneer of civilisation in Europe was paper-thin. Its collapse was mired in the mud and blood of the trenches of the Somme, Marne, Mons and Verdun. This was the first total war which saw injury and the slaughter of life on an industrial scale.

What happened in 1915 directly affected the next 100 years. Technological breakthroughs and scientific advances transformed the character of the battlefield in the 20th century, starting in World War I and accelerating in the Second. The destructiveness of national arsenals have expanded exponentially ever since.

The largest “blockbuster” bombs of World War II delivered ten tons of explosive. The atomic bomb that destroyed Hiroshima had the power of 15,000 tons of TNT. Less than 20 years later, the former Soviet Union built a nuclear bomb with the explosive force of 57 million tons of TNT. As the 20th century drew to an end – bringing with it a false dawn and the end of two competing nuclear super-powers – the world’s nearly 18,000 nuclear warheads collectively had the explosive power of 900,000 Hiroshima bombs.

Technological breakthroughs in the last 20 years have given the world cyber-warfare, unmanned drones replacing pilots roaming the globe with laser weapons to destroy ground targets, and talk of the day when robots will replace soldiers in combat.

Biological and chemical weapons continue to pose a growing threat. They are regarded as “the poor man’s bomb” because they can be built at comparatively small cost and cause widespread injury and death.

Despite the 1925 Geneva Protocol banning the use of chemical weapons in warfare, and the 1972 Biological Convention, it is known that many countries have developed several types of biological weapons. Chemical weapons have been widely used in Syria, Iraq, Iran and elsewhere in recent years. The possibility that terrorists might acquire and use such weapons poses horrific problems.

For a brief 30-year period between the mid-1960s and the early-1990s, the madness of an ever-expanding number of nuclear arsenals around the world and the growing threat of mutual destruction made co-existence and détente between the world’s super-powers essential. This led to the Nuclear Non-proliferation Treaty (NPT), which was first signed in 1968 with the aim of preventing further spread of weapons by prohibiting the transfer of nuclear weapons technology from nuclear states to non-nuclear states.

The Treaty is regarded as the cornerstone of the global non-proliferation regime and was designed not only to stop the spread of nuclear weapons, but also to advance the goal of nuclear disarmament, leading to general and complete disarmament and the promotion of cooperation in the peaceful uses of nuclear energy.

Despite the apparent success of the NPT, the obstacles to increased proliferation are fragile. The materials needed to make a nuclear weapon are widely available. The scientific expertise necessary for weapons development has spread with the globalisation of advanced scientific training. Export controls to stop technology transfer for military purposes are weak. And as we have seen with Iran (still negotiating a deal with the “Security Council nations plus Germany”) and Israel, North Korea, Pakistan, India and others, many states have strong incentives to develop nuclear weapons. And many have done so.

The 2015 Review Conference of the Parties to the Treaty on Non-Proliferation of Nuclear Weapons has just recently been held at the UN Headquarters in New York. Disappointingly, since it is the only binding commitment in a multilateral treaty to the goal of disarmament by the nuclear weapon states, the 2015 Review has ended without consensus.

At a time when Russia – still a military superpower – is again overtly reminding the world that it has a nuclear arsenal and an itchy trigger-finger, it is salutary to remind ourselves about the consequences flowing from the first use of weapons of mass destruction a century ago and whether man’s apparent drive towards self-destruction can ever be curbed.