The brigade, now composed of two battalions of the Welch Regiment and one of the Monmouthshire Regiment, together with the rest of the 53rd (Welsh) Division, was mobilised in late August 1939 and soon afterwards Britain declared war on Nazi Germany. In April 1940 160 Brigade was sent to Northern Ireland and, after the British Expeditionary Force (BEF) was evacuated from France, the brigade was mainly involved in anti-invasion duties and exercises training to repel a potential German invasion of Northern Ireland. 160 Brigade, and the rest of the 53rd Division, were sent to Southeast England almost two years later, where they began training for the eventual Allied invasion of Northern France.