The Battle of Cardiff (classified by US Army as Operation Welsh Fortress; in Ireland regarded as part of Operation Welsh Storm) was a military operation in which components of the US Army XI Corps and the US Marine Corps 2nd Division (a force totalling roughly 24,000 in number) defended the city of Cardiff and its environs from an attack by Irish Regulars, an attachment of English Workers Army infantry and armor, and the Welsh Workers Army, an associate group operation in and around the city itself.