See Dr. Art Bergeron's "Guide to Louisiana Confederate Military Units 1861-1865" (LSU Press, 1989). He presents a short history of the 12th Battalion, Louisiana Heavy Artillery on pages 11 and 12.
The battalion was organized near Yorktown, Virginia in May 1862 with two batteries from Louisiana (Orleans Parish), two batteries from Virginia, and one battery from Alabama. Company D commanded by Captain W. Norris Coffin is identified at the Bethel Artillery recruited in Virginia. Four of the companies, including Company D, were sent to Port Hudson in August 1862 and surrendered with the garrison there on July 9,1863. Those who reported for exchange were declared exchanged in the fall of 1863 and served in the defenses of Mobile until the end of the war.