Battle of Passchendaele centenary: Photos show the horrors of the First World War

The Battle of Passchendaele, one of the longest, bloodiest and most controversial battles of World War One, began 100 years ago. Also known as the third battle of Ypres, the campaign was launched on 31 July 1917 and immediately became bogged down as heavy rain turned the Flanders lowlands into a mud-churned swamp rendering tanks immobile and virtually paralysing the infantry.

The Allied forces – made up troops from Britain, France, Belgium and the British Empire (including Australia, Canada, New Zealand, South Africa and India) – aimed to capture the ridges south and east of Ypres on the Western Front from the German Empire.

Any gains they made were almost invariably soon lost, and the battle became a war of attrition. As historian Richard van Emden writes in his book The Road to Passchendaele: "1917 [was] a year of unparalleled misery on both sides of the line: an end to the war was nowhere near in sight, and popular enthusiasm for the struggle had long since eroded. The struggles ... were characterised by a grim resignation to the necessity of attrition and gradual battlefield predominance in men and arms. All in all, 1917 completed the transition to the 'wearing out' war."

The battle finally ended in appalling weather and with demoralised and tired troops after village of Passchendaele was seized by Canadian infantry in November 1917. Casualty figures are disputed, but it is thought around 310,000 Allied soldiers and 260,000 German soldiers lost their lives at Passchendaele.

The First World War, also known as the Great War, began on 28 July 1914 and lasted until 11 November 1918. It originated in Europe but became a global military conflict that killed more than 16 million people and changed the nature of warfare. On land, sea and in the air, 1914-18 was a war of new and experimental technology – technology that would increase casualty figures beyond the worst nightmares of previous conflicts.

Between 1914 and 1918, an estimated 400 million artillery rounds were fired in the narrow battlefield straddling France and Belgium.

World War One saw the introduction of many firsts in technological, scientific and societal innovations. Tanks were invented as a means of breaking the trench warfare stalemate. Chemical weapons in the form of deadly poison gases were used for the first time, leading quickly to the development of the first gas masks.