It was an infantry regiment – the 4th Rheinbund Regiment. The regiment was formed from the troops (numbers in brackets are the obligations under the Treaty) as follows: Saxe-Weimar (800 men in 5 light companies),
Saxe-Gotha (1,100 men in 8 fusilier companies),
Saxe-Meiningen (300 men in 2 fusilier companies),
Saxe-Coburg (400 men in 2 companies,
Saxe-Hildeburghausen (200 men in 1 company).
The companies from Gotha & Meiningen were to form 2 battalions and they wore the Gotha uniform. The Weimar, Hildeburghausen and Coburg troops were used to form a light battalion. Hildburghausen troops wore the Weimar uniform.
On 17 March 1807 the forces of Gotha & Meiningen were organised into a 4 company battalion – one of which was a grenadier company. 3 companies from Gotha & 1 from Meiningen. It had 14 officers and 474 men. Major von Kessel commanded.
In March 1807 the Weimar battalion was not fully incorporated into the regiment It had 24 officers and 707 men.
In late April 1807 the regiment began its first military operations when it joined the French army besieging Colberg. It was not very strong – the Weimar battalion had 270 men, and the Gotha-Miningen battalion just 224 men. On 1 May it received reinforcements of 2 companies from Gotha (1 of grenadiers) and a company from Meiningen.