In 1939, World War II erupted in Europe, and by 1940, the US Army realized that its armored warfare capabilities were inadequate should war come to America. The 4th Cavalry Regiment was redesignated as a Horse-Mechanized Corps Reconnaissance Regiment. 2nd Squadron was mechanized but 1st Squadron retained its horses until the spring of 1942 when it was mechanized as well. In January 1943, the 4th Cavalry left for the Mojave Desert to begin training for desert warfare in preparation for the fighting in the North African Campaign. Orders were changed, however, and the unit was sent to England to serve as the reconnaissance element for the VII Corps. Arriving on 15 December 1943, they camped at Singleton, West Sussex. The 4th Cavalry's designation was then changed to the 4th Cavalry Group, Mechanized (later called the 4th Mechanized Cavalry Group, or MCG. During WWII, the term MCG is synonymous with regiment in regards to cavalry formations). 1st Squadron was renamed the 4th Cavalry Reconnaissance Squadron, Mechanized, and 2nd Squadron was renamed the 24th Cavalry Reconnaissance Squadron, Mechanized.