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.

Instead, the division spent the majority of its existence guarding vulnerable points in the United Kingdom.

[3] Chamberlain had intended the agreement to lead to further peaceful resolutions to differences, but relations between both countries soon deteriorated.

[4] On 15 March 1939, Germany breached the terms of the agreement by invading and occupying the remainder of the Czech state.

[5] On 29 March, the British Secretary of State for War, Leslie Hore-Belisha announced plans to increase the part-time Territorial Army (TA) from 130,000 men to 340,000 and double the number of divisions.

[6][b] The plan was for existing TA divisions, referred to as the first-line, to recruit over their establishments, aided by an increase in pay for Territorials, the removal of restrictions on promotion which had hindered recruiting, the construction of better-quality barracks, and an increase in supper rations.

[6][13] It had been envisioned by the War Office that the duplicating process and recruiting the required numbers of men would take no more than six months.

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 second line units.

[21] Due to the lack of official guidance, the newly formed units were at liberty to choose numbers, styles, and titles.

The men of the battalion were billeted in their own homes, and attended their local drill hall for the start of their training.

[25] Training was further impeded by a large portion of the division's manpower being assigned to guarding strategically important locations, known as vulnerable points.

[11][29] In October 1939, Commander-in-Chief, Home Forces, General Walter Kirke, was tasked with drawing up a defensive plan to defend the United Kingdom from a German invasion, which was codenamed Julius Caesar.

[38][39][e] Historian David John Newbold described all forces under Kirke's command in May, including the 66th, as having "been severely weakened by departures overseas", "spread very thinly" and "largely semi-trained, relatively immobile and lacking in all types of heavy equipment, especially artillery and anti-tank guns.

[46][47][g] As a result, the 66th Infantry Division was chosen to be disbanded, which occurred on 23 June when its units were dispersed.