At dawn on the morning of November 20, 1917, six infantry and two cavalry divisions of the British Expeditionary Force—with additional support from 14 squadrons of the Royal Flying Corps—join the British Tank Corps in a surprise attack on the German lines near Cambrai, France.

After the British debuted the first armored tanks during the massive Somme offensive in September 1916, their effectiveness as a weapon–aside from the initial value of surprise–was quickly thrown into doubt. The early tanks were maddeningly slow and unwieldy; navigation and visibility from their controls were poor and though they were impervious to small arms fire, they could be destroyed easily by shellfire. Moreover, the tanks often bogged down in the muddy terrain of the Western Front in fall and winter, rendering them completely useless.

As a result, by the fall of 1917 many on the Allied side had come to doubt the viability of the tank as a major force on the battlefield. Commanders of the British Tank Corps nevertheless continued to press for a new offensive, including the large-scale use of tanks on a comparably dry stretch of battlefield in northern France, between the Canal du Nord and St. Quentin, towards the Belgian border.

After initially vetoing the idea, British Commander in Chief Sir Douglas Haig changed his mind and authorized the operation, hoping to achieve at least one useful victory before the year was out. The attack, led by General Julian Byng of the British 3rd Army, went ahead on the morning of November 20, 1917, with all available tanks–some 476 of them–advancing on the German lines with infantry, cavalry and air support. Within hours, the British forced the German 2nd Army back to Cambrai, to the north, taking some 8,000 prisoners and 100 guns on their way.

The British lacked adequate support for their initial advance, however, and more gains were significantly harder to obtain. Though German Commander in Chief Erich Ludendorff briefly considered a general withdrawal of troops from the area, his commander in the region, Georg von der Marwitz, managed to muster a sharp German counterattack of nearly 20 divisions to regain nearly all the ground lost. Casualties were high on both sides, with German losses of 50,000 compared to 45,000 for the British.

While the use of tanks at Cambrai failed to achieve the major breakthrough for which Byng had been hoping, the attack nonetheless boosted the tank’s reputation as a potentially effective weapon for targeted use during offensive operations.