The rank of lieutenant colonel has existed in the British Army since at least the 16th century and was used in both American colonial militia and colonial regular regiments. The Continental Army continued the British and colonial use of the rank of lieutenant colonel, as the second-in-command to a colonel commanding a regiment. The lieutenant colonel was sometimes known as "lieutenant to the colonel."
In British practice, regiments were actually commanded by their lieutenant colonels, as the colonel was a titular position (with the incumbent absent from the regiment serving as a senior staff officer, a general officer, or as a member of the nobility). Since the British colonel was not a "combat" officer, beginning in May 1778 to simplify prisoner of war exchanges, American regiments began to eliminate colonels by attrition and replace them with a lieutenant colonel commandant. The conversion was never completely effected and some regiments remained commanded by colonels throughout the war. From 1784 until 1791, there was only one lieutenant colonel in the US Army (Josiah Harmar), who acted as the army's commanding officer.