It was intended that the division would remain in the United Kingdom to complete training and preparation, before being deployed to France within twelve months of the war breaking out.

To boost morale, provide additional labour for the rear echelon of the BEF, and acquire political capital with the French Government and military, the division was sent to France in April 1940, leaving behind most of its administration and logistical units as well as its heavy weapons and artillery.

When Germany invaded the Netherlands and advanced into northern Belgium, the BEF and French armies moved to meet the attack, leaving the 12th Division behind.

This move intended to cut off the British and French forces in northern France and Belgium, from other formations along the Franco-German border as well as the Allied supply centres.

With no other reserves available, the 12th Division was ordered to the front line to defend several towns blocking the way between the main German assault and the English Channel.

During 1938, Germany demanded the annexation of the Sudetenland, the border areas of Czechoslovakia that were primarily inhabited by German-ethnic people.

To avoid war, the British Prime Minister Neville Chamberlain met with German chancellor Adolf Hitler in September and brokered the Munich Agreement.

[11] Despite the intention for the army to grow, a lack of central guidance on the expansion and duplication process and a dearth of facilities, equipment and instructors complicated the programme.

At that time 34,500 men, all aged 20, were conscripted into the regular army, initially to be trained for six months before being deployed to the forming second line units.

[15] Because of the lack of official guidance, the newly constituted formations were at liberty to choose numbers, styles, and titles.

[19] The war deployment plan for the TA envisioned its divisions being sent overseas, as equipment became available, to reinforce the British Expeditionary Force (BEF) that had already been dispatched to Europe.

[20] In October 1939, Commander-in-Chief, Home Forces, General Walter Kirke, was tasked with drawing up a plan, code named "Julius Caesar", to defend the United Kingdom from a potential German invasion.

The intent was that by August their job would be completed and they could return to the United Kingdom to resume training before being redeployed to France as front-line soldiers.

[34] Historian Tim Lynch commented the deployment also had a political dimension, allowing "British politicians to tell their French counterparts that Britain had supplied three more infantry divisions towards the promised nineteen by the end of the year".

He reluctantly caved to the political pressure to release the divisions, having been assured by General Sir John Gort (commander of the BEF) that the troops would not be used as frontline combat formations.

This initiated the Battle of Sedan and threatened to split the Allied armies in two, separating those in Belgium from the rest of the French military along the Franco-German border.

[38] Once the Allied commanders realised that the German crossing of the Meuse had turned into a breakthrough, the BEF and French armies began a fighting withdrawal from Belgium back to France.

The next day, Lieutenant-Colonel Robert Bridgeman, in charge of the BEF's rear headquarters, requested that Petre take command of an ad hoc force that included his 36th Brigade, a makeshift garrison in Arras and the 23rd (Northumbrian) Division.

The 7th RWK, supplemented by four field guns obtained from a Royal Artillery training school, occupied Cléry-sur-Somme to block the exits from Péronne, which had a bridge across the Canal du Nord.

The 2/6th Surrey's were ordered to move south to join the 51st (Highland) Infantry Division, but ended up being allocated to an ad hoc composition called Beauforce.

[47] Ellis wrote that the 12th Division "had practically ceased to exist", as a result of the fighting that saw the "whole tract of country between the Scarpe and the Somme" fall into German hands, and left the way to the English Channel open.

[48] Historians have praised the division for delaying the German advance for several hours, despite being under-equipped, un-prepared and fighting against unfavourable odds.

[49] The historian Gregory Blaxland was more critical, and wrote "it was both tragic and wasteful to have committed these men of little training but great spirit to battle at such hopeless disadvantage.

However, they argued that the British Army had not heeded the lessons of the invasion of Poland nor given enough thought into how infantry should counter tanks.

They believe had the battalions been concentrated and placed in more defensible positions, such as behind the Canal du Nord, they would have held greater tactical value and delayed the Germans longer than they achieved.

[58] As soon as the Allied troops returned from France, the British Army began implementing lessons learnt from the campaign.

It was re-designated the 7th Infantry Brigade in 1941, before being assigned to a variety of divisions based in the United Kingdom throughout the rest of the war.