A list of Civil War battles that Corporal Regan's infantry regiment, the 9th Mass. Vols., fought in can be found here. This list consists of the battles that the 9th Regiment participated in while in active service with the Army of the Potomac, from June 11th, 1861, to June 21st, 1864.
Corporal Regan describes all of these battles in his Civil War diaries, except for the month that Corporal Regan is captured in the Seven Days' battles at a place called Malvern Hill, and subsequently marched to Richmond Virginia to a prison camp at Belle Isle. His hardbound diary manuscript being left with a wagoner friend by the name of Hugh Dorrington for safe keeping, he keeps his diary continuous by writing on scraps of paper kept in his leggings.
You can read Corporal Regan's diary description of the battles of Gettysburg and Fredericksburg in the links provided below.
Battle Record: Ninth Massachusetts Volunteer Infantry Regiment.
Reference: "The Fighting Ninth" for Fifty Years and the Semi-Centennial Celebration. Frank J. Flynn. (out of print)
I just have to mention that if you are interested in this list of Civil War battles and the 9th Regiment, there is another excellent book with very detailed descriptions of these battles. It's called, The History of the Ninth Regiment, Massachusetts Volunteer Infantry. June 1861-June 1864. By, Daniel George Macnamara. With an introduction by Christian G. Samito.
It's a reprint of the original book from 1899 with a new introduction by Samito.
The only other book in print about the 9th Mass. Vols. is, Commanding Boston's Irish Ninth. The Civil War Letters of Colonel Patrick R. Quiney, Ninth Massachusetts Volunteer Infantry. Edited by Christian G. Samito. An excerpt from Corporal Regan's diary is in this book.
There is another book written by Michael H. Macnamara, Daniel G. Macnamara's brother, called, The Irish Ninth in Bivouac and Battle. This book was written in 1867 and is out of print. But, you can read it for free! At the above web site link. It takes you to the civil-war-irish-l. An e-mail list and forum for genealogical research and the discussion of Irish participation in the American Civil War. It is hosted by RootsWeb at no cost to subscribers.
If you found this list of Civil War battles to be informative, please click the like button! Here is another link to the Gettysburg battle description page, taken from the list of Civil War battles.