Fritz Haber, German scientist [Photographisches Institut der ETH Zürich/Wikimedia]

On April 22, 1915, Canadian and Algerian troops holding the line on the Ypres Salient watched as an ominous yellow-green cloud rose from the opposing German trenches and, carried by a light northeast wind, approached low and slow.

The cloud was, in fact, more than 160 tonnes of poisonous chlorine gas and as it rolled over the French colonials on the Canadians’ left flank, the Algerian soldiers began choking and gasping for air. Some turned and ran, but the gas followed them. The nearest Algerians made for the Canadian trenches across the road.

“Our trenches were shortly filled with them crowding in from out left,” said Lieutenant-Colonel Ian Sinclair of the 13th (Royal Highlanders of Canada) Battalion. “They were mostly blind and choking to death, and as fast as they died were just heaved behind the trench.”

The attack during the Second Battle of Ypres—the first successful incidence of modern chemical warfare—had the desired effect, opening a 6.5-kilometre gap in the Allied line, which the Canadians promptly filled as best they could. But the Germans were unprepared for such success and their advance stopped short.

Two days later, it was the Canadians’ turn as a six-metre-high wall of gas swept over their trenches north of the Belgian trade centre that had become a roadblock to the German advance to the sea. The town is known today by the Flemish Ieper (EE-per).

“The Canadians…got badly gassed,” recalled Bert Newman of the Royal Army Medical Corps. “In the end you could see all these poor chaps laying on the Menin Road, gasping for breath.”

In their first two weeks of fighting around Ypres, the Canadians suffered some 6,000 casualties, a third of the division. A thousand lay dead on the battlefield, many of them gas victims.

“On the front field one can see the dead lying here and there, and in places where an assault has been they lie very thick on the front slopes of the German trenches,” Canadian Lieutenant-Colonel John McRae wrote less than two weeks before he authored the poem, “In Flanders Fields.”

Gas attacks directly killed or wounded nearly 1.3 million soldiers in the First World War.

Fritz Haber, the German scientist who came up with the diabolical weapon, is a study in contradiction, a Jew who converted to Christianity in 1892 to secure his career, whose work not only caused misery and death to untold numbers of people in two world wars, but also saved—and continues to save—countless millions. A scientific institute in Israel bears his name.

In 1918, three years after his weapon was introduced on the battlefield at Ypres, Haber was awarded the Nobel Prize in Chemistry for developing the Haber-Bosch process, a method of synthesizing ammonia from nitrogen and hydrogen that remains fundamental to the large-scale synthesis of fertilizers—and explosives.

Developed with German chemist and engineer Carl Bosch, Hader’s fertilizer process proved a milestone in the annals of industrial chemistry. The production of nitrogen-based products such as fertilizer and chemical feedstocks, previously dependent on extracting ammonia from limited natural deposits, now became possible using an easily available, abundant base—atmospheric nitrogen.

The ability to produce far larger quantities of nitrogen-based fertilizers in turn supported much greater agricultural yields. Today, the annual world production of synthetic nitrogen fertilizer based on the Haber-Bosch process exceeds 100 million tonnes and the food base of half the world’s population depends on it.

Yet Haber was a fanatical nationalist whose chemical weapons development is said to have contributed to the May 1915 suicide of his first wife, trailblazing scientist and women’s rights activist Clara Immerwahr.

He continued working on chemical weapons even after the 1918 armistice. Two of his children killed themselves after WW II, before which Zyklon A, a pesticide developed at Haber’s institute, spawned Zyklon B, the chemical the Nazis used to exterminate more than a million Jews and other “undesirables” in the 1940s.

In a not-so-improbable twist of fate, several members of his extended family died in Nazi concentration camps.

Despite his contributions to the German cause, his Jewish ancestry caught up with him and, after 1933, Haber lived out his life in exile.

Haber once said, “during peacetime a scientist belongs to the world, but during wartime he belongs to his country.” A veteran of mandatory service 25 years earlier, Haber rejoined the military at the outbreak of WW I. He was promoted to captain and appointed head of the war ministry’s chemistry section.

He immediately assembled a team of more than 150 scientists and 1,300 technical personnel. A special gas-warfare troop was formed (Pioneer Regiments 35 and 36) under the command of Otto Peterson. Haber and Friedrich Kerschbaum served as advisers. Haber recruited physicists, chemists and other scientists to the cause.

Future Nobel laureates James Franck, Gustav Hertz (both in physics) and Otto Hahn (chemistry) served as gas troops in Haber’s unit. Haber seized on chlorine gas largely because it was heavy and settled downward. His teams also developed other deadly chemicals for use in trench warfare, including mustard gas.

Haber was on hand when the chlorine was released outside Ypres. He defended the weapon against accusations that it was inhumane, saying that death was death, regardless of how it was inflicted.

In his studies of the weapon’s effects, Haber noted that exposure to a low concentration for a long time often had the same effect—death—as exposure to a high concentration for a short time. He formulated a simple mathematical relationship between the gas concentration and the necessary exposure time. This relationship became known as Haber’s rule.

Haber died in January 1934, at just 65 years old. He has remained the object of much criticism from the science community for his involvement in developing chemical weapons.

Yet in 1981, the Minerva Foundation of the Max Planck Society and the Hebrew University of Jerusalem established the Fritz Haber Research Center for Molecular Dynamics, based at the Institute of Chemistry of the Hebrew University. Its purpose is the promotion of Israeli-German scientific collaboration in the field of molecular dynamics. The centre also houses the Fritz Haber Library.