fusileers
According to "Foot regiments of the Imperial Guard"by Michael Head the fusileers chasseurs were raised october 19, 1806; the fusileer-grenadiers december 15, 1806. So the chasseurs would be the first.
Also is stated that the fus-chasseurs comprised 2 battallions, each 4 companies for a total regimental strenth of 1200 men. No strength is given for the fus grenadiers but I suppose they are the same.
Mentioned is, that in 1811 each batt received a 5th company (called fusiliers-sergeants) and in december 1813 a 6th company was added to each battalion.
With 6 companies in each battalion (and each company probably the same strenth as the first companies namely 150) the theoretical strenth of the regiment would be 1800 men. Maybe the mentioned strenth comes from this.
greetings
jan