The frock coat was adopted by every major army in the 19th century. Here is how they used it.
Quick answer. Military frock coats followed civilian cut but added regimental facings, braid, piping and buttons. British officers wore scarlet or dark blue frock coats as undress. American Civil War officers on both sides wore dark blue (Union) or grey (Confederate) frock coats. French officers wore dark blue; Russian wore dark green; German wore dark blue. All used the frock coat for staff, social and campaign dress between about 1830 and 1900.
British military frock coats
British officers from the 1830s onwards wore a frock coat as the undress uniform. Infantry officers in scarlet with regimental facings. Rifle officers in dark green. Cavalry officers in dark blue, scarlet or black depending on regiment. The frock coat was worn for staff work, social events, church parade and all occasions where the full dress coatee was not required. By 1850 it was the dominant daily officer's garment. By 1900 it was giving way to the service dress tunic and khaki field uniform.
The British military frock coat had regimental details: facings at collar and cuff, specific button patterns, regimental lace at the back of the collar and sleeve. Rank was shown by epaulettes, cuff lace or shoulder cords depending on regiment and period. Field officers added additional lace at the collar and cuff.
The Union frock coat
United States officers in the Civil War wore a dark blue frock coat with gilt buttons and shoulder straps for rank. Infantry had sky blue trim at the collar and cuff; cavalry had yellow; artillery had red. Enlisted men wore a shorter dark blue shell jacket, but officers wore the full frock. General officers wore a double breasted frock coat with buttons arranged in rows (two for brigadier, three for major general, four for lieutenant general). Lincoln is shown in portraits in a civilian version of the same silhouette.
The Confederate frock coat
Confederate regulations prescribed a grey frock coat with branch colour trim: sky blue for infantry, yellow for cavalry, red for artillery. Buttons were gilt with a state or branch design. Shoulder marks and sleeve lace indicated rank (one, two or three Austrian braid knots on the sleeve for junior, field and general officers). In practice supply shortages meant Confederate officers wore every grade of coat from fine imported English wool to home spun butternut dyed cloth. The classic Confederate officer image, Robert E. Lee in grey frock coat with three Austrian knots, remains iconic.
French and other European frock coats
French officers wore the redingote, essentially a frock coat, from the 1830s. Dark blue with gold or silver buttons and rank marks on the sleeve or epaulette. Russian officers wore a dark green frock coat with branch colour trim. German officers wore a dark blue frock coat often with heavy braid at the collar and cuff. The frock coat was universal across European armies by 1860. Each adopted the civilian pattern and added national distinctions.
The move away from the frock coat
From the 1880s most armies began replacing the military frock coat with a shorter tunic for field use. The British adopted the khaki service dress tunic from 1902. The French kept the redingote longer but shortened the skirt. The Germans introduced the shorter Waffenrock. By 1914 the military frock coat was essentially gone from the field, though it survived in some ceremonial and senior staff positions. Today the British Army still issues a scarlet frock coat to Guards officers for certain mess occasions.
Common questions
Did American Civil War soldiers wear frock coats?
Officers on both sides did. Enlisted men mostly wore shorter shell jackets or sack coats, though some enlisted men were issued frock coats.
What is Austrian braid?
A pattern of knots in gold or silver cord on the sleeve of a frock coat. Used by Confederate officers to show rank: one knot for lieutenants, two for field officers, three for generals.
What is a redingote?
The French word for a frock coat, derived from the English riding coat. Used both in civilian and military dress through the 19th century.
Can I buy a replica military frock coat?
Yes. Civil War, Victorian British and other military frock coats are built by specialist tailors in wool with hand set buttons and lace. Allow six to twelve weeks of lead time.
Is any military frock coat still worn today?
The British Guards officers' scarlet frock coat is still issued for mess dress and some ceremonial. The Danish Royal Life Guards wear a frock coat for parade dress. Other ceremonial frock coats survive in older European military traditions.