The Auxiliary Air Force dates back to the 1920s. In 1925, AAF 502 (Ulster) Squadron made history, becoming the first of 21 Special Reserve Squadrons.
World War Two began on 3rd September 1939. By October that year, the first waves of British Army infantry troops had begun to arrive in Northern Ireland.
Towards the end of the Second World War, there were many German prisoners of war in Northern Ireland in camps and military hospitals across the country.
The Mechanised Transport Corps based in Belfast, Co. Antrim operated under the Ministry of Supply. The volunteers wore battledress and held officer status.
RAF 303 and 315 Squadrons represented the Polish Air Force during the Second World War in Northern Ireland. Both units flew from RAF Ballyhalbert, Co. Down.
During World War Two, the Royal Air Force operated from airfields across Northern Ireland providing bases for training, U-Boat patrols, and convoy escorts.
Many personnel from the Royal Australian Air Force died in Northern Ireland while training in Royal Air Force training units during the Second World War.
During the Second World War, many members of the Royal New Zealand Air Force served in R.A.F. Squadrons and Training Units across Northern Ireland.
The first troops of the United States Army to enter the European Theatre of Operations landed at Dufferin Dock, Belfast, Co. Antrim on 26th January 1942.
The Women's Royal Naval Service (WRNS) reformed in 1939 at the beginning of the Second World War and at its height in 1944 had 75,000 active servicewomen.