For two weeks, the Canadian Corps has been barrelling through the canals, rivers, trenches, bunkers and barricades of the Hindenburg Line , suffering terrivble losses but advancing quickly for the first time in this war. Today's objective is Cambrai, on the other side of the Escaut Canal system, and the 4th Battalion, Canadian Engineers, has the job of keeping three bridges at Pont-d'Aire intact for the advance. It is 2:30 a.m.

Explosives expert Captain Coulson Mitchell, who earned the Military Cross as a tunneller, is assigned to the main bridge, which comprises two 75-foot steel girder spans on stone abutments and a centre pier, with a concrete deck about 15 feet above the tow-path. Captain Mitchell and his men, Sergeant E. Jackson, Sapper L.G. Brewer and Sapper E.C. Murphy, quietly examine the bridge: when they find German grenades, they know it is wired to blow. With Spr Murphy and Spr Brewer on guard, Capt Mitchell and Sgt Jackson locate the wiring and follow it to a large boxed charge on the nearest girder; the other girders, they know, are similarly prepared. Using the scaffold abandoned by the German demolition party, the Canadians are hard at work cutting wires when they suddenly hear rifle fire; the Germans have realized what is happening, and Spr Brewer is fighting them off. When Capt Mitchell and Sgt Jackson join the battle, two Germans are already dead and Capt Mitchell kills a third; the fazed Germans withdraw, giving Spr Murphy time to fetch their infantry covering party. When the Germans renew their attack, the infantry have their Lewis gun ready.

While the battle rages on the bridge deck, Capt Mitchell and Sgt Jackson work, removing the grenades from the rails and about 500 pounds of explosives from the girders. By 4:00 a.m., the infantry are across the bridge, with the field artillery hard on their heels.

For this action, Capt Mitchell is awarded the Victoia Cross, thus becoming the only Canadian sapper to receive this distinction. Sgt Jackson and Spr Brewer each receive the Distinguished Conduct Medal.

"Fourth Dimension" is a regular feature written for the Canadian Forces
newspaper The Maple Leaf, published by the Department of National Defence.