The Fifth Army was a field army of the British Army during World War I that formed part of the British Expeditionary Force on the Western Front between 1916 and 1918. The army originated as the Reserve Corps during the preparations for the British part of the Somme Offensive of 1916, was renamed Reserve Army when it was expanded and became the Fifth Army in October 1916.

Operation Michael was a major German military offensive during the First World War that began the German Spring Offensive on 21 March 1918. It was launched from the Hindenburg Line, in the vicinity of Saint-Quentin, France. Its goal was to break through the Allied (Entente) lines and advance in a north-westerly direction to seize the Channel Ports, which supplied the British Expeditionary Force (BEF), and to drive the BEF into the sea. Two days later General Erich Ludendorff, the chief of the German General Staff, adjusted his plan and pushed for an offensive due west, along the whole of the British front north of the River Somme. This was designed to first separate the French and British Armies before continuing with the original concept of pushing the BEF into the sea. The offensive ended at Villers-Bretonneux, to the east of the Allied communications centre at Amiens, where the Allies managed to halt the German advance; the German Army had suffered many casualties and was unable to maintain supplies to the advancing troops.