A dress uniform is for being seen; a service uniform is for being used. The gap between them has shaped military tailoring for 300 years.
Quick answer. Dress uniform is parade and ceremonial wear: scarlet tunics, bullion epaulettes, feather bonnets, bearskins, swords. Service uniform is the working kit: khaki, olive drab, DPM, or the modern No 4 service dress. Full dress is almost extinct outside ceremonial units; service dress is universal. Mess kit, patrol dress and barrack dress sit in between.
A short history of the split
Until 1800, armies had one uniform. It was worn on parade and into battle. By 1850, the gap between parade and field had opened: the British army had Full Dress (scarlet, bearskin, white gloves) and Undress (dark blue frock coat, forage cap). The Crimean War 1854 to 1856 widened the gap further, as service dress proved impossible in the field.
By 1902, after the Boer War, khaki service dress was universal in the British army, and the scarlet of the regular line was reserved for the Household Division. The modern six category system (full dress, service dress, mess dress, barrack dress, combat dress, PT dress) was fixed in 1947 with Dress Regulations. Our British parade dress piece covers Full Dress today.
Full dress: the showiest kit
Full dress is the surviving ceremonial uniform. In the British army today it is worn by the Household Division (bearskin, scarlet, blue trousers with a red stripe), the Royal Horse Guards (blue, cuirass, white plume), the Royal Horse Artillery, the Royal Military Academy, the massed bands and the Royal Regiment of Scotland in Highland dress.
The French army uses it in the Garde Republicaine (helmet, cuirass, white breeches) and the Legion Etrangere (kepi blanc, red epaulettes). The US army uses it in the Old Guard and the Caisson Platoon. In most other units full dress is gone, replaced by ceremonial service dress or by mess kit. Our 19th century parade dress piece covers how the Victorian version worked.
Service dress: the working uniform
Service dress is the daily working uniform of a soldier not in the field. In the British army it is No 2 Dress (service dress tunic, trousers, side cap) or No 4 (same cut, warmer colour). It is olive drab khaki, cut like a plain lounge suit, with regimental buttons and shoulder titles.
Service dress began as khaki drill in 1902, driven by Boer War experience and the sniper threat. It replaced scarlet for field use entirely. The modern No 2 is worn to work, to funerals, to court martials, and to civilian ceremonies where combat dress would be inappropriate. See our British 19th century military uniforms piece for the long transition.
Mess dress: the dinner uniform
Mess kit sits between full dress and service dress. It is dinner wear: a short tailed scarlet or blue mess jacket, white or regimental coloured waistcoat, dark trousers with regimental stripes, bowtie, miniature medals, and highly polished shoes. It derives from the Victorian officers' mess uniform of the 1880s.
Each regiment has its own mess kit specification. The 11th Hussars had crimson overalls (hence the Cherrypickers nickname). The Royal Marines wear a scarlet mess jacket. The Royal Navy wears a short blue monkey jacket. Our Victorian mess dress piece covers the origin and modern form.
Barrack dress and combat dress
Barrack dress is working wear inside the barracks: a wool pullover over a shirt, trousers, boots. It is the uniform of a soldier doing admin, teaching recruits, or standing by at camp. The British No 13 Working Dress is a classic example.
Combat dress is the field uniform. Multi Terrain Pattern (MTP) camouflage, body armour, boots, helmet. It is the uniform of actual soldiering. In the field, every other category is irrelevant. Nothing on it shines, nothing stands out, nothing says anything except the shoulder flash.
Which is the real uniform
The question has no answer. Full dress carries the regiment's history and shows the organisation to the public. Service dress carries the soldier through the working day. Mess dress binds the officer corps together over dinner. Combat dress keeps him alive in the field.
What is universal is that an officer carries all four or five uniforms, maintained to a high standard, and knows which to wear and when. The private soldier is issued the equivalent at government expense (except mess dress, which is private purchase). For a full map of the British system, our British military uniforms guide covers the whole landscape.
Common questions
What is the difference between full dress and service dress?
Full dress is ceremonial, derived from pre 1900 field uniform (scarlet, bearskin, white gloves). Service dress is the modern khaki working uniform, cut like a lounge suit.
When was khaki service dress adopted?
1902 in the British army, after the Boer War. It replaced scarlet for field use entirely by 1914.
What is mess kit?
The officers' dinner uniform. Short tailed scarlet or blue jacket, regimental waistcoat, dark trousers with regimental stripe, bowtie, miniature medals.
Who still wears full dress today?
The Household Division, Royal Horse Guards, Royal Military Academy Sandhurst, French Garde Republicaine, US Old Guard, and the ceremonial troops of most monarchies.
What is combat dress?
The field uniform: camouflage, boots, body armour, helmet. In the British army currently Multi Terrain Pattern (MTP). The only one of the six categories designed to be invisible.