On 22 August 1939, just before the outbreak of war, Fullbrook-Leggatt was promoted to the temporary rank of brigadier and was given command of the 184th Infantry Brigade, part of the 61st Infantry Division, then commanded by Major General Robert Collins. The brigade was a second line Territorial Army (TA) formation, only very recently formed as a duplicate of the 145th Infantry Brigade, and was composed largely of part-time civilian soldiers. The outbreak of war saw the brigade mobilised for full-time war service, and training for eventual overseas service in France with the British Expeditionary Force (BEF), although the German invasion of France in May 1940 forestalled this, and the brigade, along with the rest of the 61st Division, now commanded by Major General Adrian Carton de Wiart, moved to Northern Ireland, after the BEF was evacuated from France and there was a possibility of the Germans invading the United Kingdom through Southern Ireland (see Operation Green).