Franco-Irish Ambulance Brigade

The Franco-Irish Ambulance Brigade (known in French as the Ambulance Irlandais) was a volunteer medical corps sent from Ireland to assist the French Army in the 1870–71 Franco-Prussian War. At the time Ireland was part of the United Kingdom of Great Britain and Ireland and parliament had passed the Foreign Enlistment Act 1870 which, in most circumstances, prohibited British citizens from enlisting in foreign armies.

Source: Wikipedia — Franco-Irish Ambulance Brigade (CC BY-SA 4.0)