The 3rd (Ulster) Searchlight Regiment 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 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.

3rd Anti-Aircraft Brigade was a Supplementary Reserve air defence formation of the British Army formed in Northern Ireland in 1938. On the outbreak of the Second World War it saw active service with the British Expeditionary Force during the Battle of France and Operation Aerial. It then returned to Northern Ireland and defended the Province for the next two years. Postwar, it was reformed in the Territorial Army and served until the disbandment of Anti-Aircraft Command in 1955.