Prior to this, European soldiers, infantry, cavalry and artillery had worn open dress uniform coats with turn-back lapels over either coloured or white sleeved-waistcoats and breeches.
The advent of closed uniform coatees, i.e. waist- length jackets with standing collars and tails, buttoned from throat to waist, meant that sleeved waistcoats could not be worn underneath and therefore fell redundant.
However, in order to save damage or staining to dress coatees while on fatigue duties, etc., a new, relatively plain coloured waist-length jacket was introduced.
During the first half of the 19th Century, the British Army wore dress coatees in battle against Europeans or Americans, but tended to wear shell jackets on colonial campaigns.
Cavalry and artillery shell jackets remained in use until after the American Civil War as they were more practical for mounted troops than the long frock (which was briefly introduced in 1851 but rejected).