Charles Erskine 5th Earl of Mar was appointed as the regiments first Colonel on 23 September 1678. The regiment first saw action at the Battle of Bothwell Bridge on 22 June 1679. In 1685 it was engaged in suppressing the rebellion of the Earl of Argyle. Then in 1686 Thomas Buchan became colonel of the regiment. In 1688 the regiment left Scotland and marched to England in support of King James, against the Prince of Orange. After the change of power, Thomas Buchan was dismissed and succeeded by Francis Fergus O'Farrell by commission of 1 March 1689.
The regiment was sent overseas almost immediately, sailing from Gravesend, (my hometown), in March 1689 to form part of the allied force defending the Low Countries, opposing Louis XIV of France. The force included (Treasury Books for 25th January 1689/90) the 2nd troop of Guards and Grenadiers; the Royal Regiment of Horse; the Royal Regiment of Scots Footguards; Royal Regiment of Fusiliers; the Regiments of Foot commanded by Col. Charles Churchill, Col. John Hales, Sir David Coliear, Col. Edward FitzPatrick, Col Robert Hodges and Col. Francis D’O’Farrell. The army was under the command of Prince Waldeck, and the regiment served in the division under Earl (as he then was) Marlborough.
They fought at Walcourt in on 25th August 1689, Shortly afterwards the regiment was issued with the new flintlock muskets (in about 1690), hence being named the Scots Fusiliers by Royal Warrant.
On 27th July 1691 they were drawn up at Gerpines Camp, where their uniforms were described as “red, lined red”. They next fought at Steenkirk (or Steenkerke) on 3rd August 1692, a hard-fought but indecisive engagement. Some weeks before that battle, O’Farrell was taken prisoner by the French while on his way to a conference with the Duke of Wurtemburg (Duke Eberhard Louis, who served under William in Ireland as well as on the Continent), but was released on payment of the customary ransom. On 29th July 1693 they fought at Landen (Neerwinden), when the French forces under Marshall Luxembourg defeated William’s forces.
During 1694 O’Farrell was appointed commander of the town of Diense in the Low Countries, one of a chain of fortified towns across the Low Countries which were fought over by the French and English. When the town was besieged on 21st July 1695 by Villeroy’s army O’Farrell surrendered to the French without firing a shot, and he was tried by a court-martial on 19th October . He was perhaps lucky, because the commander of Dixmude (which had been taken by Villeroy on his way to Diense), who surrendered at the same time, was beheaded!
The 21st Fusiliers, were then bestowed on Col. Robert McKay on 13th November 1695, he died in December 1696. Then in 1697 Archibald Row, formerly Lieutenant-Colonel of Stanley's regiment became the new Colonel. After the peace of Rijswijk the regiment was shipped to Scotland. Row's regiment survived the 1699 disbandings on the Scottish establishment.