Upon the expiration of term of service of his Regiment he was formerly mustered-out, but immediately re-commissioned Captain in the 121st New York Volunteers, and continued on the staff as before. When Colonel Upton became General Bartlett's successor in command of the Brigade, he was placed on his staff. He is highly complimented in the report by this latter officer of his command in the battle of Rappahannock Station, November 7th, 1863. "From my own staff I received, in every instance, prompt and gallant assistance, and to their united efforts may be attributed, in a great measure, the promptness with which both regiments re-formed inside the works. Captain H. Seymour Hall, Assistant Inspector General, entered the rifle pits with the men." After this engagement he was promoted to ACTING ASSISTANT ADJUTANT GENERAL on the staff of this Brigade commander, which position he held in connection with the other until his commission in this Regiment. It may not be improper to introduce here a few extracts of communications setting forth the high appreciation of Colonel Hall for his ability and bravery, by very competent Judges. Brigadier General Jackson, Commander of 2nd Brigade, 2nd Division, 12th Corps, in his letter addressed to Adjutant General of the State of New York, requesting the appointment of Captain Hall to Colonel of the 145th New York Volunteers, which Regiment was in his Brigade, and without a Colonel, states: "I have known Captain Hall for the past fifteen months, and consider him every way qualified to fill the above mentioned position." Major General Slocum's endorsement on this paper testifies: "I know Captain Hall to be a capable, efficient and faithful officer, and most cordially unite with General Jackson in this recommendation." Major General Slocum himself, also, in a letter relating to the same subject, and addressed to the same Officer of State, closes with the remarks: "I am well acquainted with him (Captain Hall,) and know him to be a capable and efficient officer, and think his appointment would be a great benefit to the service. Captain Hall has no knowledge of my intention to recommend him for this position, and in doing it I am only actuated by a desire to improve the condition of the troops under my command." For some reason or other, left unsatisfactory unexplained, the State Executive made no appointment whatever. In consequence of this the Regiment alluded to was obliged to forego its organization, and be consolidated with others.