[3] At Arras the Canadians were to capture Vimy Ridge, dominating the Douai Plain to the east, advance towards Cambrai and divert German reserves from the French front.

[5] The previous year had been marked by the costly success of the Anglo-French offensive astride the River Somme, while the French had been unable to take the initiative because of intense German pressure at Verdun until after August 1916.

[5] The cost to Germany of containing the Anglo-French attacks had been enormous and given that the material preponderance of the Entente and its allies could only be expected to increase in 1917, Field Marshal Paul von Hindenburg and General Erich Ludendorff decided on a defensive strategy on the Western Front for that year.

[7] This impasse reinforced the French and British commanders' belief that to end the stalemate they needed a breakthrough; while this desire may have been the main impetus behind the offensive, the timing and location were influenced by political and tactical considerations.

In March, the German army in the west (Westheer), withdrew to the Hindenburg line in Operation Alberich, negating the tactical assumptions underlying the plans for the French offensive.

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.

[22] In a new manual published on 1 December 1916 by Oberste Heeresleitung (OHL, supreme command of the German army), Grundsätze für die Führung in der Abwehrschlacht im Stellungskrieg (Principles of Command for Defensive Battles in Positional Warfare), the policy of unyielding defence of ground, regardless of its tactical value, was replaced by the defence of positions suitable for artillery observation and communication with the rear, where an attacking force would "fight itself to a standstill and use up its resources while the defenders conserve[d] their strength".

[24] Allgemeines über Stellungsbau (Principles of Field Fortification) was published by OHL in January 1917 and by April an outpost zone (Vorpostenfeld) held by sentries, had been built along the Western Front.

During the Battle of the Somme in 1916 Colonel Fritz von Loßberg (Chief of Staff of the 1st Army) had been able to establish a line of relief divisions (Ablösungsdivisionen), with the reinforcements from Verdun, which began to arrive in greater numbers in September.

Loßberg considered that spontaneous withdrawals would disrupt the counter-attack reserves as they deployed and further deprive battalion and division commanders of the means to conduct an organised defence, which the dispersal of infantry over a wide area had already made difficult.

Sceptics wanted the tactic of fighting in the front line to continue, with authority devolved no further than battalion, to maintain organizational coherence in anticipation of a methodical counter-attack (Gegenangriff) by the relief divisions after 24–48 hours.

[27] General Ludwig von Falkenhausen, commander of the 6th Army arranged the infantry at Arras for the rigid defence of the front-line, supported by methodical counter-attacks (Gegenangriffe), by the "relief" divisions (Ablösungsdivisionen) on the second or third day.

The subterranean workings were lit by electricity and supplied by piped water, with gas-proof doors at the entrances; telephone cables, exchanges and testing-points used the tunnels, a hospital was installed and a tram ran from the sewer to the St Sauveur caves.

In one sector, four Tunnelling companies of 500 men each, worked around-the-clock in 18-hour shifts for two months to dig 12 mi (20 km) of subways for foot traffic, tramways with rails for hand-drawn trolleys and a light railway system.

Four tanks were to attack Neuville Vitasse, four against Telegraph Hill, four against The Harp and another four against Tilloy lez Mofflaines and two were to drive down the slope from Roclincourt west of Bois de la Maison Blanche.

[11] German casualties were not heavy but the men became exhausted by the endless task of keeping open dug-out entrances and demoralised by the absence of rations caused by the difficulties of preparing and moving hot food under bombardment.

[46] Zero-Hour had originally been planned for the morning of 8 April (Easter Sunday) but it was postponed 24 hours at the request of the French, despite reasonably good weather in the assault sector.

The combination of the unusual bombardment and poor visibility meant many German troops were caught unawares and taken prisoner, still half-dressed, clambering out of the deep dugouts of the first two lines of trenches.

[50] Military historians have attributed the success of this attack to careful planning by Canadian Corps commander Julian Byng and his subordinate General Arthur Currie,[51] constant training and the assignment of specific objectives to each platoon.

By giving units specific goals, troops could continue the attack even if their officers were killed or communication broke down, thus bypassing two major problems of combat on the Western Front.

Battalions of pioneers built temporary roads across the churned up battlefield; heavy artillery (and its ammunition) was manhandled into position in new gun pits; food for the men and feed for the draught horses was brought up and Casualty Clearing Stations were established in readiness for the inevitable counter-attacks.

[54] The news of the battle reached General Ludendorff during his 52nd birthday celebrations at his headquarters in Kreuznach who wrote, "I had looked forward to the expected offensive with confidence and was now deeply depressed".

On their left, the 37th Division, attacked the buildings west of Roeux Station and gained the line of their objectives on the western slopes of Greenland Hill, north of the railway.

Several determined German counter-attacks were made and by the morning of 24 April, the British held Guémappe, Gavrelle and the high ground overlooking Fontaine-lès-Croisilles and Cherisy; the fighting around Roeux was indecisive.

[59] The principal objective of the attack was to tie down German reserves to assist the French offensive against the plateau north of the Aisne traversed by the Chemin des Dames.

Haig reported, With a view to economising my troops, my objectives were shallow and for a like reason and also in order to give the appearance of an attack on a more imposing scale, demonstrations were continued southwards to the Arras–Cambrai Road and northwards to the Souchez River.

[61] After securing the area around Arleux at the end of April, the British determined to launch another attack east from Monchy to try to break through the Boiry Riegel and reach the Wotanstellung, another German defensive position in the Douai Plain.

[62] The Hindenburg Line defences enclosing the village of Bullecourt formed a re-entrant for about 2,500 yd (2,286 m) to the Balkonstellung (Balcony Trench) around Quéant, defended by the élite German 27th Division.

Captain Cyril Falls, the author of the History of the Great War volume on the battle (1940), estimated that 30 per cent needed to be added to German returns for comparison with the British.

[85] Loßberg was soon promoted to general and directed the defensive battle of the 4th Army against the Flanders Offensive of the summer and late autumn; he had become "legendary as the fireman of the Western Front; always sent by OHL to the area of crisis".