A retirement could disrupt the British offensive at Arras and Franco-British planning gained urgency as a German withdrawal became likely in February and March, according to the results of air reconnaissance, agent reports and gleanings from prisoners.

These arrangements were maintained until 24 February, when German local withdrawals in the Ancre valley, required the Fifth Army divisions to make a general advance to regain contact.

The ground in the Ancre valley was in the worst condition, a wilderness of mud, flooded trenches, shell-hole posts, corpses and broken equipment, overlooked and vulnerable to sniping from German positions.

Constant rain wet the ground so badly, that horses drowned and men became stuck up to their waists; in December ropes were issued to drag soldiers out of the mud.

"Elephant" shelters (the materials for which took ten men to carry forward and 24 hours to build) were placed in the front-line, sunk below trench and shell-hole parapets.

The division wore highland kilts, which left the top of the leg bare underneath and their boot edges chafed the skin and caused septic sores, until 6,000 pairs of trousers were issued.

Quartermasters improvised large numbers of extra cookers, so that the troops in the line could eat hot food when they pleased but the improvements made little difference to sickness.

Company strengths had declined to 50–60 men, so thinly spread that a stray German was taken prisoner near a brigade headquarters, having seen no sign of British troops until he was captured.

The 2nd Division continued to consolidate the positions begun earlier, large working parties labouring non-stop to dig out, clean and pump trenches, fit duckboards and provide overhead cover for the infantry posts; tramways were built further back by engineers.

Conditions were worse if possible, than those on the south side of the Ancre valley, causing much sickness despite precautions like rubbing whale oil into the feet to prevent trench foot and bringing dry socks up with the rations.

At 5:30 p.m. fifty British troops attacked up Serre Trench and along the ground on either side as fast as they could through the mud, re-capturing the post, taking nine prisoners for one casualty.

White suits were provided in case of snow and all means of identification were to be removed by the raiders, who were told only to give name, rank and number if captured.

[20] As a preliminary to capturing the Loupart Wood line (Riegel I Stellung), Gough intended the Fifth Army to continue the process of small advances in the Ancre valley.

[21] The II Corps artillery began destructive and wire-cutting bombardments on 14 February, using ammunition with the new fuze 106 against the German wire, which proved effective, despite fog and mist making aiming and observation of the results difficult.

[21] A thaw set in on 16 February and at dawn there were dark clouds overhead and mist on the ground, which turned soft, slippery then reverted to deep mud.

The 53rd Brigade on the left flank had a wider front, much of which was also exposed to fire from the positions on the north bank due to be attacked by the 63rd (Royal Naval) Division and was to consolidate on the second objective.

The defenders were alert and inflicted many casualties with small-arms fire; the darkness, fog and the sea of mud slowed the advance and caused units to become disorganised.

The creeping barrage moved at 100 yd (91 m) in four minutes, slower than on the south bank and the Germans in a small number of strong points were quickly overcome.

A section of 8-inch howitzers was available for the bombardment of strong points and road junctions and the XIV Corps heavy batteries were able to neutralise German artillery during the attack.

[32] A 400 yd (370 m) length of Stormy Trench was attacked by part of a battalion of the 2nd Australian Division late on 1 February, which took the left-hand section and bombed down it to take the rest, before being forced out by a German counter-attack at 4:00 a.m.

[34] In February, instructions were issued from the divisional headquarters covering communications, supply dumps, equipment, arms and ammunition to be carried by each soldier, the proportion of the attacking units to be left out of battle, medical arrangements, substitute commanders, liaison, wire-cutting and bombardment arrangements of SOS signals for artillery and machine-gun barrages, gas bombardment, smoke screens and measures to deal with stragglers and prisoners.

The instructions went into great detail, stipulating that officers were to dress the same as their men, precautions were to be taken to stop machine-gun barrages falling on friendly troops, the positions of observers and the calculation of safety distances.

The morale of British as well as German units had suffered and special arrangements were made to collect "stragglers" at brigade and divisional posts, where soldiers names were to be taken, before being rearmed and equipped with items taken from wounded troops in Advanced Dressing Stations.

British arrangements for holding captured ground worked well and a German battalion in a wood near Moislains preparing to counter-attack was dispersed by the machine-gun barrage with 400 casualties.

German artillery-fire on the captured area, on the former no man's land and around Bouchavesnes caused considerably more casualties when two communications trenches were being dug to link the new positions with the old British front line.

[38] The Royal Flying Corps undertook a considerable tactical reorganisation after the battle of the Somme, according to the principles incorporated in documents published between November 1916 and April 1917.

[43] The retirement was conducted in a slow and deliberate manner, through a series of defensive lines over 25 mi (40 km) at the deepest point, behind rear-guards, local counter-attacks and the demolitions of the Alberich plan.

The QF 4.5-inch howitzer was to be used for neutralising German artillery with gas shells, bombarding weaker defences, blocking communication trenches, night barrages and wire-cutting on ground where field guns could not reach.

Artillery boards came into use, which had blank sheets with a 1:10,000 scale grid in place of maps, datum shooting was used to check gun accuracy from two to three times a day and better calibration drills and meteor (weather) telegrams were announced.

[58] The Australian official historian, Charles Bean, wrote that the advanced troops of I Anzac Corps had gone out on a limb, which had led to the reverse at Noreuil on 20 March, after instructions from the Fifth Army headquarters to press forward to the Hindenburg Line, were misinterpreted.