Firelock companies were raised throughout the Civil Wars for a variety of purposes. Formed originally to fight in the wild bogs of Ireland where a flintlock was more easily handled than the clumsy matchlock, firelock-armed musketeers grew more common as the Civil Wars progressed, all armies sometimes fielding large units so armed.
The firelock had numerous advantages over the older matchlock. It was ready to fire at a moment's notice, was more weatherproof and did not betray a night advance with glowing match cord. It was also much cheaper in the long run as they did not consume vast quantities of match cord.
They were regularly used for baggage and artillery guards, as the flintlock mechanism was seen as infinitely more desirable in a gunpowder depot than spluttering, lit, match cord!
By mid to late war, whole companies were fielded. For the Royalists, Legge's who fought at Edgehill, Rupert’s and Maurice’s redcoats and Sandford's from Ireland. Parliament issued them liberally and many of the New Model Army had whole companies so armed and later, whole regiments. The Scots Covenanter forces also used the firelock to good effect.
Warlord Games’ Firelocks are shown storming a bridge led by their dashing Captain, just the sort of action that Firelock Companies were used for!