In March 1918, the German Army advanced closer to Amiens and Paris and Denning's unit was sent to France to help stop the advance. Under continuous shell fire for three months, the company and the 38th (Welsh) Infantry Division held their section of the line, with a unit under Denning's command building a bridge to allow infantry to advance over the River Ancre. Denning went two days without sleep while building these bridges; shortly after one was completed, a German aeroplane dropped a bomb on it, forcing them to start again. The unit advanced over the River Ancre and the Canal du Nord, but Denning fell ill with influenza and was in hospital for the last few days of the war. When writing of his experiences in World War I in "The Family Story", Denning summed up his war service with characteristic pithiness in just four words: "I did my bit".