Some 150,000 Irish-American immigrants served in the Union Army, most of them from Boston, New York and Chicago, and about 40,000 fought in the Confederate Army. Out of the array of Irish-American units involved in the conflict, perhaps the best known was the Irish Brigade of the Union Army of the Potomac, which distinguished itself at both Antietam and, particularly, at Fredericksburg, where its sacrificial bravery astonished friend and foe alike. Other famous regiments were New York's 'Fighting 69th', the 9th Massachusetts, 116th Pennsylvania, 23rd Illinois and 35th Indiana whilst several other Irish companies made a name for themselves at Shiloh, Chickamauga and other key battles. This book provides a brief overview of the history of the units on each side of the conflict and a comprehensive survey of all Irish-American units in both Union and Confederate armies, from brigade down to company size. Rare early photographs are a poignant addition to the story of the immigrants caught up in a vicious civil war, and detailed colour plates illustrate unit distinctions and flags in a book that is essential reading for any Civil War enthusiast.