In 1910, after the formation of the Ceylon Defence Force, the CLIV became a part of it and was renamed the Ceylon Light Infantry. With the outbreak of World War II, CLI was mobilized and consisted of two battalions and was under the command of Lieutenant Colonel John Kotelawala. The CLI soon expanded and was deployed for home defense and overseas in the Seychelles and the Cocos Islands. The third battalion was raised in 1941, a fourth battalion in late 1942, and a fifth battalion in April 1943. One battalion each was deployed at Colombo, Kandy and Trincomalee, with the fourth fourth battalion under training and one battalion reserved for special duties. Soon after the war a regular element of the regiment was formed to take up garrison duties in Ceylon. This unit was named the Mobilised Detachment of Ceylon Light Infantry (Mob. Det., CLI).