On the night of 8 April 1917, as the Battle of Arras began, the 10th Battalion attacked Louverval Wood, an outpost of the Hindenburg Line of German defences. McCann was wounded in the neck during the attack, and after having it bandaged and being scarcely able to speak, remained with his troops for several hours, and according to the "Australian Dictionary of Biography", "was an inspiration to his men". Once the situation was clear, he reported for medical attention and was evacuated to hospital in England. After six weeks recuperating, McCann rejoined his unit at the end of May, assuming command of A Company. He remained with the battalion throughout the Battle of Passchendaele in Flanders from July to November 1917, including the Battle of the Menin Road Ridge in September, before being seconded to a training battalion in the United Kingdom in late December. He returned to his battalion in June 1918. On 29 June, after the battalion had captured a section of the German line using "peaceful penetration" tactics, McCann's company was in the newly won positions when the Germans counter-attacked and got between his advanced posts. He led his company signallers, messengers and reserve platoon forward into the gap. The Germans dropped their weapons, which included a machine gun, and ran.