In the pre-Norman days of Ireland, young warriors who left home to join warrior cults would often band together, forming groups known as ceithearn, or warbands. The individual soldiers, known as ceithearnach, would typically be lightly armed, and rarely wore armor of any kind. This would form the template for the island’s native light infantry for years to come.

After the arrival of the English, the term became kern, which could refer to either the lightly armed mercenary forces in the region, or the soldiers that made up those forces. In the late 12th century, a kern was a small band of about twenty mercenaries under an independent captain. These kerns would travel the countryside looking for employment, intimidating the peasantry to make ends meet. Over time, kern came to simply mean “troops”, and referred to the bulk of the Irish military, particularly those skirmishers who fought largely unarmored, armed with a sword and throwing darts. Paid half of what was earned by foot archers, the kerns were at their best when set to harassing civilians, plundering cattle, and burning houses.

By the late 16th century, English authors described the Irish forces as consisting of kerns, native cavalry, and foreign mercenaries known as Gallowglasses. The latter two groups were well respected by the English. The kerns, however, were not. One author’s contempt led him to refer to them as “scum” and “a generation not fit to live”.

On their helmets and shields Duna’s warriours ring
The hail-storm of war from the bow and the sling.
Nor shun the close conflict–but what may avail
The kerns’ naked breasts ‘gainst the knights clad in mail?

-William Hamilton Drummond, Bruce’s Invasion of Ireland; A Poem 1826