Editing First day on the Somme (section)

====Intelligence====

{{see also|Brusilov Offensive}}

In March and April, eight German divisions were believed to be in reserve opposite the British from the Somme to the North Sea coast. Divisions in reserve behind the [[4th Army (German Empire)|4th Army]] were then moved south to Artois in the 6th Army area. From 4 to 14 June, the success of the [[Brusilov Offensive]] became apparent and agent reports showed increased railway movement from [[Belgium]] to [[Germany]]. The final BEF military intelligence estimate before 1 July had {{nowrap|32 German}} battalions opposite the Fourth Army and {{nowrap|65 battalions}} in reserve or close enough to reach the battlefield in the first week. Five of the seven German divisions in reserve had been engaged at Verdun and some divisions had been transferred from France to the [[Eastern Front (World War I)|Eastern Front]]. Men of the 1916 conscription class were appearing among German [[prisoners of war]], suggesting that the German army had been weakened and that the British could break down the German front line and force a battle of manoeuvre on the defenders. In late June, the British part of the Somme plan was amended, rapidly to capture Bapaume and envelop the German defences northwards to [[Arras]], rather than southwards to [[Péronne, Somme|Péronne]]. An increase in the number of trains moving from Germany to Belgium was discovered but the quality of German troops opposite the British was thought to have been much reduced. The true number of German divisions in reserve in France was ten, with six opposite the British, double the number the British knew about. Reports of work continuing on the German defences opposite the Fourth Army in March and April led the planners to adopt a less optimistic view, particularly due to the news about very deep shell-proof shelters being dug under German front trenches, which were far less vulnerable to bombardment.{{sfn|Beach|2004|pp=160–163}}