Attack on Hindenburg line
With 'land battleships (tanks) in the background, this image shows infantry advancing during the attack on the famous Hindenburg Line. As the Hindenburg Line was finally overrun by the Allies in the autumn of 1918, it seems highly likely that this is when this photograph was taken.
The Hindenburg Line was a massive system of German fortifications that extended to a depth of 15 kilometres, rather than just a shallow line of trench defences. These fortifications ran all the way along the Western Front, stretching from the northern coast to Verdun. The decision in September 1916 to build these defences was crucial, since it showed that the German generals were preparing to fight a defensive war. As there were no strong back-up lines behind the Hindenburg Line, once it had been breached, retreat was the only viable option left. (Hindenburg Line = a system of German defence fortifications behind the northern and central sectors of the Western Front, constructed between the northern coast and Verdun.)
[Original reads: 'OFFICIAL PHOTOGRAPH TAKEN ON THE BRITISH WESTERN FRONT IN FRANCE. Attack on Hindenburg line. Tanks and Troops advancing.']