From 29 September to 1 October 1918, Wark assumed temporary command of the 32nd Battalion, leading the unit in the 5th Division's attack against the Hindenburg Line at Bellicourt (part of the Battle of St Quentin Canal), and the subsequent advance through Nauroy, Etricourt, Magny La Fosse and Joncourt. This series of battles became the 32nd Battalion's final actions for the war, and it was during this period that Wark earned his Victoria Cross.
The 32nd Battalion was to commence its attack at Bellicourt at 09:00 on 29 September, and move south through the village. Due to mist and smoke from a preceding artillery barrage, visibility was poor. When the advance was held up by two German machine guns, Wark ordered a tank to neutralise them. On reaching the southern end of St Quentin Canal tunnel, Wark came across two hundred troops of the American 117th Infantry Regiment who appeared to be leaderless, and attached them to his own command. A short time later, with visibility still poor, he appropriated armoured reinforcements and began an advance on the village of Nauroy. As the fog began to lift, Wark organised his troops for an attack on the village from a southerly direction. By 11:30, the battalion had taken the village, along with forty Germans as prisoners of war.
Shortly afterwards, Wark observed a battery of German 77 mm guns firing on his rear companies, causing heavy casualties. Collecting a party of his men, he rushed the battery and succeeded in capturing four guns in conjunction with ten crewmen. With only two men, he pushed forward and surprised fifty Germans near Magny-la-Fosse who subsequently surrendered. At 15:00, he halted his battalion near Joncourt, and sent out patrols which found the town still occupied by enemy forces. The 32nd Battalion responded by withdrawing slightly and strengthening its line. At 17:30, the Germans launched a counter-attack that was repulsed with the assistance of the 31st Battalion, together with some men from the 46th (North Midland) Division.
At 07:00 the next day, the 32nd Battalion attacked once more, advancing 1,500 metres (1,600 yd) to a point just north of Etricourt. Under heavy shelling and machine gun fire, they established a line between Joncourt and Etricourt. On 1 October, at 06:00, with a company attached from the 30th Battalion, the 32nd Battalion launched an attack that cut through Joncourt. Leading from the front, Wark dashed forward and silenced machine guns that were causing heavy casualties; this enabled the 5th Division to complete its task of forcing through to the Beaurevoir Line.
The full citation for Wark's Victoria Cross appeared in a supplement to the London Gazette on 26 December 1918, reading:
War Office, 26th December, 1918
His Majesty the KING has been graciously pleased to approve of the award of the Victoria Cross to the undermentioned Officers, N.C.O.'s and Men: —
Maj. Blair Anderson Wark, D.S.O., 32nd Bn., A.I.F.
For most conspicuous bravery, initiative and control during the period 29th Sept. to 1st Oct. 1918, in the operations against the Hindenburg Line at Bellicourt and the advance through Nauroy, Etricourt, Magny La Fosse and Joncourt.
On 29th Sept., after personal reconnaissance under heavy fire, he led his command forward at a critical period and restored the situation. Moving fearlessly at the head of, and at times far in advance of, his troops, he cheered his men on through Nauroy, thence towards Etricourt. Still leading his assaulting companies, he observed a battery of 77mm. guns firing on his rear companies and causing heavy casualties. Collecting a few of his men, he rushed the battery, capturing four guns and ten of the crew. Then moving rapidly forward with only two N.C.O.s, he surprised and captured fifty Germans near Magny La Fosse.
On 1st Oct., 1918, he again showed fearless leading and gallantry in attack, and without hesitation and regardless of personal risk dashed forward and silenced machine guns which were causing heavy casualties.
Throughout he displayed the greatest courage, skilful leading and devotion to duty, and his work was invaluable.