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On November 20, 1917, the British army gained more ground in six hours than in six months at Passchendaele. The target was the Hindenburg Line near Cambrai, a German rail hub, defended by deep trenches, concrete bunkers and dense wire. Artillery commander Henry Tudor relied on predicted fire, aiming guns by calculation for wind, temperature, pressure, shell weight and barrel wear, with German batteries located by low-frequency sound-ranging microphones. The No. 106 fuse burst shells on contact, cutting wire without cratering the ground, while Hugh Elles’s Tank Corps led the infantry.

More than 1,000 guns opened fire without warning, and about 437 Mark IV tanks advanced up to five miles beside six divisions. Then the plan unraveled. A bridge at Masnières collapsed under a tank, Field Artillery Regiment 108 under Major Krebs knocked out nearly 40 tanks at Flesquières, and the 40th Division lost over 4,000 men in Bourlon Wood. On November 30 German stormtroopers using Hutier infiltration tactics struck the salient, and by December the battle ended in a draw costing over 100,000 casualties.

• Of 180 tanks out of action on day one, only 65 were destroyed by enemy fire.
• Major General Harper kept the 51st Highland Division’s infantry too far behind its tanks.
• The legend of a lone German gunner at Flesquières hides a trained anti-tank unit.
• Brigadier General Berkeley Vincent fought his way out of his own headquarters.
• Eight British machine guns at Bourlon fired 70,000 rounds, boiling their cooling water.