As he climbed to the top of the church belfry in Bolimow, west of Warsaw, General Max Hoffman of Germany's Ninth Army was expecting a bird's-eye view of a military breakthrough - and a new chapter in warfare.

The date was 31 January 1915, and he was about to witness the first major gas attack in history.

Gen Hoffman watched as 18,000 gas shells rained down on the Russian lines, each one filled with the chemical xylyl bromide, an early form of tear gas. But the results left him disappointed.

"I had expected much greater results from the employment of this ammunition in - as we then imagined - such large quantities. That the chief effect of the gas was destroyed by great cold was not known at that time."

But the failure at Bolimow proved to be only a temporary setback....