5927376 Comparative aerial photographs of Passchendaele, 1 October and 12 November 1917 (b/w photo) by Unknown photographer, (20th century); National Army Museum, London; (add.info.: Comparative aerial photographs of Passchendaele, 1 October and 12 November 1917. Photograph, World War One, Western Front (1914-1918), 1917. The Third Battle of Ypres (or Passchendaele) was launched on 31 July 1917. The operation aimed to drive a hole in the enemy lines, capture the high ground around the city of Ypres, advance to the Belgian coast and capture the ports, thus removing the German submarine menace. Foul weather and strong German resistance, including the use of mustard gas, saw the offensive grind to a halt in a shell-churned and water-logged wasteland. By the time the Canadians had captured the town of Passchendaele on 6 November, the British had advanced 8 kilometres (5 miles). Commonwealth losses approached 300,000. German casualties were 260,000. The battle of attrition almost broke the resolve of both armies.); by National Army Museum .