In 1917, during the First World War, the armies on the Western Front continued to change their fighting methods, due to the consequences of increased firepower, more automatic weapons, decentralisation of authority and the integration of specialised branches, equipment and techniques into the traditional structures of infantry, artillery and cavalry. Tanks, railways, aircraft, lorries, chemicals, concrete and steel, photography, wireless and advances in medical science increased in importance in all of the armies, as did the influence of the material constraints of geography, climate, demography and economics. The armies encountered growing manpower shortages, caused by the need to replace the losses of 1916 and by the competing demands for labour by civilian industry and agriculture. Dwindling manpower was particularly marked in the French and German armies, which made considerable changes in their methods during the year, simultaneously to pursue military-strategic objectives and to limit casualties.

The French returned to a strategy of decisive battle in the Nivelle Offensive in April, using methods pioneered at the Battle of Verdun in December 1916, to break through the German defences on the Western front and return to a war of manoeuvre () but ended the year recovering from the disastrous result. The German army attempted to avoid the high infantry losses of 1916 by withdrawing to new deeper and dispersed defences. Defence in depth was intended to nullify the growing material strength of the Allies, particularly in artillery and succeeded in slowing the growth of Anglo-French battlefield superiority. The British Expeditionary Force (BEF) continued its evolution into a mass army, capable of imposing itself on a continental power, took on much of the military burden borne by the French and Russian armies since 1914 and left the German army resorting to expedients to counter the development of its increasingly skilful use of fire-power and technology. During 1917 the BEF also encountered the manpower shortages affecting the French and Germans and at the Battle of Cambrai in December, received its biggest German attack since 1915, as German reinforcements began to flow from the Eastern Front.

Background Paul von Hindenburg and Erich Ludendorff replaced Chief of the General Staff Erich von Falkenhayn on 19 August 1916, during "the most serious crisis of the war". On 2 September the new leadership ordered a strict defensive at Verdun and the dispatch of forces from there to reinforce the Somme and Romanian fronts. Hindenburg and Ludendorff visited the Western front and held a meeting at Cambrai on 8 September with the army group and other commanders, at which the gravity of the situation in France and the grim prospects for the new year were debated. Hindenburg and Ludendorff had already announced a reconnaissance on 6 September for a new, shorter line behind the Noyon salient. On 15 September a defensive strategy was announced except for Romania and Rupprecht (commander of the northern army group on the Western front) was instructed to prepare a new line, Arras–St. Quentin–Laon–Aisne river.

The new line across the base of the Noyon salient would be about shorter and was to be completed in three months. These defences were planned with the experience gained on the Somme, which showed a need for much greater defensive depth and many small shallow concrete -- ( shelters), rather than elaborate entrenchments and deep dug-outs, which had become man-traps. Work began on 23 September; two trench lines about apart were dug as an outpost line () and a main line of resistance () on a reverse slope, () behind fields of barbed wire up to deep. Concrete machine-gun nests and shelters were built either side of the main line, with artillery observation posts built farther back to overlook it.

On 31 August, Hindenburg and Ludendorff had begun the expansion of the army to and of munitions production in the Hindenburg Programme, necessary to meet demand after the vast expenditure of ammunition in 1916 (on the Somme in September, artillery shells and shells had been fired) and the anticipated increase in artillery use by the Allies in 1917. It was intended that the new defensive positions would contain any Allied breakthrough and give the German army the choice of a deliberate withdrawal, to dislocate an expected Allied offensive in the new year. Over the winter of 1916–1917, the wisdom of a deliberate withdrawal was debated and at a meeting on 19 December, called after the 15 December during the Battle of Verdun, the possibility of a return to the offensive was also discussed. With a maximum of expected to be available by March 1917, a decisive success was considered impossible.

Ludendorff continued to vacillate but in the end, the manpower crisis and the prospect of releasing thirteen divisions by a withdrawal on the Western Front, to the new (Hindenburg line), overcame his desire to avoid the tacit admission of defeat it represented. The (Alberich manoeuvre) was ordered to begin on 16 March 1917, although a withdrawal of on a front had already been carried out from 22 to 23 February, in the salient between Bapaume and Arras, formed by the Allied advance on the Somme in 1916. The local retirements had been caused by the renewal of pressure by the British Fifth Army, as soon as weather permitted in January 1917, which had advanced on a front up the Ancre valley.

German defensive preparations, early 1917

Third OHL

On 29 August 1916, Hindenburg and Ludendorff had been appointed to the (OHL, supreme army command) of the German army, after the sacking of Falkenhayn, who had commanded the armies of Germany since September 1914. The new commanders, who became known as the Third OHL, had spent two years in command of , the German section of the Eastern Front. Hindenburg and Ludendorff had demanded reinforcements from Falkenhayn to fight a decisive campaign against Russia and intrigued against Falkenhayn over his refusals. Falkenhayn held that decisive military victory against Russia was impossible and that the Western Front was the main theatre of the war. Soon after taking over from Falkenhayn, Hindenburg and Ludendorff had no choice but to recognise the wisdom of Falkenhayn's judgement that the Western Front was decisive, despite the crisis in the east caused by the Brusilov Offensive (4 June – 20 September) and the Rumanian declaration of war on 28 August.

Cambrai conference

On 8 September 1916, Hindenburg and Ludendorff held a conference at Cambrai with the chiefs of staff of the armies of the as part of a tour of inspection of the Western Front. Both men were dismayed at the nature of trench warfare that they found, in such contrast to the conditions on the Eastern Front and the dilapidated state of the . The Battle of Verdun and the Battle of the Somme had been extraordinarily costly and on the Somme, casualties had been suffered from 24 June to 28 August. The battle had required the use of and by September, one division a day had to be replaced by a fresh one. General Hermann von Kuhl the Chief of Staff of (Army Group German Crown Prince) reported that conditions at Verdun were little better and that the recruit depots behind the army group front could supply only of the casualty replacements needed. From July to August the had fired the equivalent of of field gun shells, for the receipt of only Germany, creating a munitions shortage.

The 1st Army on the north side of the Somme reported on 28 August that,

It was known in Germany that the British had introduced conscription on 27 January 1916 and that despite the huge losses on the Somme, there would be no shortage of reinforcements. At the end of August, German military intelligence calculated that of the divisions in France, fresh. The French manpower situation was not as buoyant but by combing out rear areas and recruiting more troops from the colonies, the French could replace losses until the 1918 conscription class became available in the summer of 1917. Of the divisions in France, in reserve and another 10 to 11 divisions could be obtained by swapping tired units for fresh ones on quiet parts of the front.

Ludendorff admitted privately to Kuhl that victory appeared impossible, who wrote in his diary that

On 29 August, Hindenburg and Ludendorff reorganised the army groups on the Western Front, by incorporating all but the 4th Army in Flanders into the army group structure on the active part of the Western Front. The administrative reorganisation eased the distribution of men and equipment but made no difference to the lack of numbers and the growing Franco-British superiority in weapons and ammunition. New divisions were needed and the manpower for them and the replacement of the losses of 1916 had to be found. The superiority in manpower enjoyed by the Entente and its allies could not be surpassed but Hindenburg and Ludendorff drew on ideas from (Lieutenant-Colonel) Max Bauer of the Operations Section at OHL HQ in Mézières, for a further industrial mobilisation, to equip the army for the (battle of equipment/battle of attrition) being inflicted on it in France, which would only intensify in 1917.

Hindenburg Programme

The new programme was intended to create a trebling of artillery and machine-gun output and a doubling of munitions and trench mortar production. Expansion of the army and output of war materials caused increased competition for manpower between the army and industry. In early 1916, the German army had in recruit depots and another in March when the 1897 class of conscripts was called up. The army was so flush with men that plans were made to demobilise older classes and in the summer, Falkenhayn ordered the raising of another for an army of The costly battles at Verdun and the Somme had been much more demanding on German divisions and they had to be relieved after only a few days in the front line, lasting about on the Somme. A larger number of divisions might reduce the strain on the and realise a surplus for offensives on other fronts. Hindenburg and Ludendorff ordered the creation of another to reach by early 1917.

The men for the divisions created by Falkenhayn had come from reducing square divisions with four infantry regiments to triangular divisions with three regiments, rather than a net increase in the number of men in the army. Troops for the extra divisions of the expansion ordered by Hindenburg and Ludendorff could be found by combing out rear-area units but most would have to be drawn from the pool of replacements, which had been depleted by the losses of 1916 and although new classes of conscripts would top up the pool, casualty replacement would become much more difficult once the pool had to maintain a larger number of divisions. By calling up the 1898 class of recruits early in November 1916, the pool was increased to in February 1917 but the larger army would become a wasting asset. Ernst von Wrisberg, of the (head of the Prussian Ministry of War section responsible for raising new units), had grave doubts about the wisdom of the increase in the expansion of the army but was over-ruled by Ludendorff.