According to US Army regulations, officers coats were to be dark blue frock coats reaching down about 2/3s of the way between the waist and the knee. The coat has a standing collar and three small brass buttons on each cuff. The skirts of the frock coats also had pockets in them. Company grade (junior grade) officers' frock coats had one row of nine medium size brass buttons and shoulder straps to indicate rank. The background color of the shoulder straps indicated the branch of service of the officer: red for Artillery, sky blue for Infantry, yellow for Cavalry. Above, we see two examples of field grade officers uniforms. The figures in the photo above are of officers of the 1st Connecticut Heavy Artillery at Fort Brady, Virginia in 1864. The third figure in the photo is wearing a officer's grade sack coat. This may have been custom tailored. Officers sometimes wore these in the field instead of their frock coats.
Field grade officers' (Majors, Colonels) regulation frock coats were of the same length and cut of the company grade coats. The difference between these types of frock coats was that it had 2 rows of 7 buttons each. Majors and Lt. Colonels all had the same arrangement: 7 equal spacing. Generals had 2 rows of 8 buttons or 3 rows of 9 buttons. The picture above is of General Jefferson C. Davis and his staff outside of Washington DC. You can see good examples of both types of officer's frock coats with a couple of officer sack coats thrown in. You will also notice that a couple of the figures in the photo have piping on the seam of their pant legs. The piping according to regulations was to be1/8" wide and would be the color designated for the branch of service. You will also notice the mixture of headgear on the figures in this photo. You will notice the M-1858 Hardee Hat and the officer's version of the forage cap. There are also a casual version of the Hardee Hat called a slouch hat . Just like the enlisted man's uniform the officer's manner of dress reflected the attitude of the man in it.
Mounted officers and officers of the light artillery were allowed to wear single or double breasted waist length coats. The single breasted coats resembled company grade officer's frock coats without the skirts. The single breasted jacket had 1 row of medium size brass buttons down the front and 3 small buttons on each cuff. The double breasted coats resembled the field grade officer's frock coats with two rows of 7 medium brass buttons. Light artillery officers were also allowed by General Order 20 written in 1860 to wear 'Russian' shoulder knots with their rank insignia in silver on the trefoil end. The photo above is of 6 officers from the 17th New York Battery. It was taken in June or July of 1863 near Gettysburg Pa. The officer second from the left is wearing a single breasted coat as is the man on the far right. Five of the 6 officers are also wearing their officer sashes and are carrying 3 different types of swords which was typical. There is also a mix of sky blue and dark blue pants.