In September 1939 the Second World War commenced between the UK and its allies against Germany. In December 1941 the Japanese entered the war when it launched a surprise attack on Pearl Harbor and launched a number of swift invasions of British and other countries territories. During the course of the war the Regiment raised a further three battalions, the 3rd in 1940, the 4th in 1941 and the 5th in 1942; the Regiment saw much service in the war but most notably in Malaya and Burma.