The 3rd (Ulster) Searchlight Regiment (3rd (Ulster) S/L Rgt) was a Supplementary Reserve (SR) unit of the Royal Artillery raised in Northern Ireland just before the outbreak of World War II. It distinguished itself in the Battle of France before being evacuated from Dunkirk. It then served in Anti-Aircraft Command, converting into the 4th (Ulster) Light Anti-Aircraft Regiment (4th Ulster LAA Rgt) in 1942. In that role it served in the campaign in North West Europe, defending Brussels against V-1 flying bombs. It was reformed postwar and its successor units continued to serve in the Territorial Army (TA) until 1993.