The 4th Royal Lancashire Militia (The Duke of Lancaster's Own Light Infantry) was an auxiliary regiment raised in the county of Lancashire in North West England just before the Crimean War. It later became part of the South Lancashire Regiment. Although primarily intended for home defence, it saw considerable active service during the Second Boer War. After conversion to the Special Reserve (SR) under the Haldane Reforms it supplied reinforcements to the fighting battalions during World War I and carried out internal security duties in Ireland. After a shadowy postwar existence the unit was finally disbanded in 1953.