According to the general order, there was allowed to each regiment one chaplain, who was appointed by the regimental commander on the vote of the field officers and company commanders on duty with the regiment at the time the appointment is to be made. The chaplain so appointed must be a regularly ordained minister of some Christian denomination, and will receive the pay and allowances of captain of cavalry.
The first chaplain of the 13th Maine was Henry D. Moore, a Congregationalist Minister from Portland. However, during the hurricane encountered on their trip south he behaved in such a cowardly and unprincipled manner that he was discharged by an outraged General Benjamin Butler (he left the stricken ship on a rescue craft with Gen. Butler's wife contrary to Butler's specific orders not to). In fact, Butler suggested that the ship's captain execute him for disobeying orders and cowardly desertion, but he was allowed to leave with his life. But the official records indicate it was a disability discharge and not an act of cowardice - Moore must have had friends with the influence to do that because Butler would never have forgiven his behavior.
Lufkin is much more circumspect and discrete in his treatment of the instance... "Next morning (3/1/1862), after a survey of the injured vessel, it was decided to go to Port Royal, South Carolina, for repairs. All who had been transferred to the Mount Vernon were returned to the Mississippi, except one staff officer of the 13th Maine who, although like a guide-post pointing the way to heaven, apparently had no personal desire to go there by water! He remained on the uninjured vessel and sent in his resignation, which was promptly accepted by Gen. Butler."
An interim chaplain was Charles E. Blake, a Free Will Baptist Clergyman from Farmington, Maine. He enlisted as a private into Co. K on 12/13/1861 and was promoted to chaplain on 3/23/1862. He was discharged on 8/18/1863.
I have found no record of a regimental chaplain from 8/18/1863 until 4/4/1864.
Another chaplain was Josiah Keeley, a Baptist Clergyman from Saco, Maine, but born in England. He enlisted as a chaplain on the regimental staff at Saco, Maine, on 3/3/1864 and mustered in at Natchitoches, Louisiana, on 4/4/1864. He died of malarial fever at St. James Hospital, New Orleans, Louisiana, on 6/24/1864 while the regiment was at Morganza, Louisiana. Both of his sons, Hospital Steward George Keeley, and Lieutenant William Keeley served in the 13th Maine with him and survived the war.
The last chaplain was William Willis Hayward, a Universalist Minister from Fairfield, Maine. He enlisted as a chaplain on 9/26/1864 at Fairfield, Maine, and mustered in at Augusta, Maine, on 9/26/1864. He mustered out with the regiment with an honorable discharge at Augusta, Maine, on 1/6/1865.