text: Strategy The French, Russians and British had intended to launch a joint spring offensive in 1917 but this strategy foundered in February when the Russians admitted that they could not meet their commitments. The spring offensive was reduced from attacks on the Eastern and Western fronts to a French assault along the Aisne River. In March, the German army in the west (), withdrew to the Hindenburg line in Operation Alberich, negating the tactical assumptions underlying the plans for the French offensive. Until French troops advanced into the former Noyon Salient during the Battles of Arras, they encountered no German troops in the assault sector and French doubts over the wisdom of the offensive increased. The French government desperately needed a victory to avoid civil unrest but the British were wary of proceeding, given the rapidly changing tactical situation. In a meeting with Lloyd George, French commander-in-chief General Robert Nivelle persuaded the British Prime Minister, that if the British launched a diversionary assault to draw German troops away from the Aisne sector, the French offensive could succeed. It was agreed in the London Convention of 16 January, that the French assault on the Aisne would begin in mid-April and that the British would make a diversionary attack in the Arras sector approximately one week prior.
  Tactics: British Expeditionary Force
  Three of the armies of the British Expeditionary Force (BEF, Field Marshal Sir Douglas Haig) were in the Arras sector, the Fifth Army (General Hubert Gough) in the south, the Third Army (General Edmund Allenby) in the centre and the First Army (General Henry Horne) in the north and the plan was devised by Allenby. The British used the lessons of the Somme and Verdun the previous year and planned to attack on an  front, from Vimy Ridge in the north to Neuville-Vitasse,  south of the Scarpe river. The preliminary bombardment was planned to last about a week except for a much longer and heavier barrage at Vimy Ridge.