Thinking about the "British Grenadiers". I'd reckon it's pretty well definite that it refers to the "new" arm of service when grenades came into use around the mid 1600's or so, and companies were formed in line regiments. Don't the verses talk about "leaders march with fusees / and we with hand grenades"? By the time the Grenadier guards were a separate unit, the actual use of the primitive grenade had pretty well ended - around the 1750's (?), but the name was retained for those sections acting as stormtrooper squads or light companies for the regular infantry. The grenade didn't make a real re-appearance until the 1914-18 war