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.

This separation impeded the division's ability to train, leaving the formation ill-trained and ill-prepared by the time the Battle of France begun.

The fighting in France resulted in the surrender of the majority of the 51st (Highland) Infantry Division, with only elements of one brigade able to escape to Britain.

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

[9] On 29 March, British Secretary of State for War Leslie Hore-Belisha announced plans to increase the size of the Territorial Army (TA), a reserve force of the regular army made up of part-time volunteers, from 130,000 to 340,000 men and double the number of TA divisions.

This resulted in 34,500 twenty-year-old men being conscripted into the regular army, initially to be trained for six months before deployment to the forming second-line units.

Some TA divisions had made little progress by the time the Second World War began; others were able to complete this work within a matter of weeks.

[26] The division's first general officer commanding (GOC) was Major-General George Lindsay, who had been called out of retirement.

[27] Rosyth would remain an important base for the RN, and home to one of four naval shore commands that were established, responsible for control of coastal waters and inspecting intercepted shipping.

The division's brigades were not kept intact, and the infantry battalions were dispersed across Scotland to protect these RN assets.

[34] The remaining battalion, the 7th Black Watch, was dispersed to protect vulnerable points around Fife and Perthshire, including the Forth Bridge.

[34] In October 1939, Commander-in-Chief, Home Forces Walter Kirke was tasked with drawing up a defensive plan to defend the United Kingdom from a German invasion, which was codenamed Julius Caesar.

Kirke dismissed the feasibility of such an attack, and believed that East Anglia or the south coast were the areas in imminent danger of invasion as a result of the German operations on mainland Europe.

In his words "... strong points prepared for all-round defence at aerodromes ... at the main centres of communication, and distributed in depth over a wide area covering London and the centres of production and supply" with the intent of preventing "the enemy from running riot and tearing the guts out of the country as has happened in France and Belgium.

The division assisted in the construction of beach obstacles, rigged bridges for destruction and established roadblocks.

The latter, on 6 May 1940, had been assigned to the French sector of the front near Saarland, between Colmen and Launstroff, and positioned on the frontline between the border and the Maginot Line.

Under French command, the division was withdrawn towards the Somme after initial engagements with German forces on the border.

Due to thick fog, which impeded the ability of ships to approach, and German guns that had been positioned to dominate the port, the division was unable to escape and was forced to surrender on 12 June.

The historian Craig F. French wrote that the loss of the 51st "came as 'another Flodden' to the Scots nation", gave the men of the 9th (Highland) a desire to avenge their comrades, and resulted in a "profound difference in the attitude of all ranks towards the need for training.

[56] The 154th, which had been under direct War Office control before being assigned to Scottish Command following its escape from France, absorbed the 28th Brigade.

[57][58] French wrote, before the renaming of the division, that due to it being "stationed over a wide area, [it] did not have the opportunity to coalesce into a cohesive unit with its feelings of wider divisional loyalties.

[55] The new 51st (Highland) Division would go on to fight in the Western Desert campaign, notably at the Second Battle of El Alamein.