In 1803, the contingent of the two principalities were reorganized in four infantry battalions :

Following the Austrian system, each battalion was composed of a company of grenadiers and three companies of musketeers , each of :| 1 | Hauptmann | | 1 | Oberleutnant | | 2 | Leutnants | | 1 | Felwebel | | 4 | Sergeants | | 8 | Korporals | | 8 | Gefreiten | | 2 | Trommler | | 120 | Soldaten |
These battalions were organized in the Nassau infantry brigade that took part in 1806 to the Prussian campaign.
In June 1808, battalions were reorganized along the French system of one grenadier, one voltigeur and four fusilier companies and regrouped in two infantry regiments, the 1st Nassau Infantry Regiment receiving the two Usingen battalions and the 2nd one the Weilburg battalions.
The 2nd Nassau Infantry Regiment was posted at the end of 1808 in Leval German Division and fought in Spain until 1813 when he went over to the British in July. The 1st Nassau Infantry Regiment took part in the Austrian campaign and was sent to Catalonia at the beginning of 1810. He was disarmed and interned after 2nd regiment defected.

Infantry brigade 1806-1807

Fusiliers

I. (Leib-) Bataillon

• Single breasted long tailed coat in dark green cloth closed by a row of 7 buttons. Scarlet collar laced light orange bearing two light orange buttonhole laces. Scarlet shoulder straps trimmed light orange. Front of coat piped in light orange. Scarlet rounded cuffs laced light orange bearing two light orange buttonhole laces, one on cuff and one above. Scarlet turnbacks piped light orange, vertical pockets bearing four light orange buttonhole laces. Brass buttons.
• White vest. Light grey breeches bearing black Hungarian knots and dark grey knee length gaiters. In summer dress, white overalls and gaiters.
• Black leather Bavarian style helmet with black wool crest bearing a brass grenade badge. Brass front band and side struts. Black plume. Black leather peak with brass strengthening.
• Yellow leatherwork. Black leather cartridge pouch bearing a brass oval plate stamped with Nassau lion. Infantry sabre with brass hilt and black leather scabbard with brass fittings.

II. Bataillon

• Same coat as 1st battalion with brick red facings. No buttonhole laces on collar or cuffs.
• Grey vest. Grey breeches bearing red Hungarian knots and grey knee length gaiters. In summer dress, white overalls and gaiters.
• Black felt shako with black leather top and bottom bands. Black plume over yellow pompon over black cockade. Yellow cords and flounders. Black leather peak.
• Same equipment as 1st battalion.

III. (Jäger-) Bataillon

• Same coat as 2nd battalion with bright red facings. White metal buttons.
• Green vest. Grey breeches bearing red Hungarian knots and grey knee length gaiters. In summer dress, white overalls and gaiters.
• Black felt shako with black leather top and bottom bands. Black plume over black cockade. white cords and flounders. Black leather peak.
• Black leatherwork. Same equipment as 1st battalion.

IV. Bataillon

• Same coat as 2nd battalion with crimson facings.
• White vest. Grey breeches bearing black Hungarian knots and grey knee length gaiters. In summer dress, white overalls and gaiters.
• Shako as 2nd battalion covered with grass green, green plume and pompon.
• Same equipment as 1st battalion.

Grenadiers

• I. (Leib-) Bataillon : Fusiliers’ dress with scarlet plume and red laced gaiters.
• III. (Jäger-) Bataillon : Black felt cocked hat. Yellow wool pompon over black cockade laced white. White wool tassels. Black leather cartridge box worn on stomach. Hunter sabre with brass hilt and black leather sheath with brass fittings.
• IV. Bataillon : Fusiliers’ dress. On shako, brass grenade badge and large bushy red plume, scarlet cords and flounders. Heart shaped gaiters with red lace and tassel.

NCOs
Troopers’ dress with gold (brass buttons) or silver (white metal buttons) lace on front and bottom sides of collar and on cuffs.

Drummers
Troopers’ dress with facings coloured swallow nests laced yellow and six yellow chevrons on both arms. Seven yellow buttonholes laces on front of coat. Copper drums stamped with Nassau lion and hoops painted with alternate yellow and blue triangles.

Infantry regiments, transition dress 1808-1809

Fusiliers

• Single breasted coat in dark green cloth closed by a row of 7 buttons. Black collar laced light orange. Black shoulder straps trimmed light orange. Front of coat piped in light orange. Black rounded cuffs laced light orange. Black turnbacks piped light orange. Brass buttons.
• White vest. Grey breeches bearing black Hungarian knots and black knee length gaiters.
• Black felt shako with black leather top and bottom bands, bearing a brass trophy of arm plate with dice cut regimental number. Company coloured (1st yellow, 2nd white, 3rd sky blue, 4th black) tufted pompon over black cockade. White cords and flounders. Black leather peak and brass chinscales.
• Yellow leatherwork and black leather cartridge pouch.

Grenadiers
1st battalion of both regiments : Fusiliers’ dress with same buttonhole laces and helmet as former Leib-Bataillon. Scarlet fringed epaulets. Brass grenade badge on pouch and infantry sabre with scarlet sabre strap.
2nd battalion of both regiments : Fusiliers’ dress with brass grenade badge on shako. Scarlet plume, cords, flounders and fringed epaulets Brass grenade badge on pouch and infantry sabre with scarlet sabre strap.

Voltigeurs
Fusiliers’ dress with brass horn badge on shako. Green plume, cords, flounders and fringed epaulets Brass horn badge on pouch and infantry sabre with green sabre strap.

NCOs
Troopers’ dress with yellow or gold rank laces on both arms.

Officers
Other ranks’ dress with gold laces and epaulets. Gilded gorget bearing a silver lion. Green cloth breeches, black leather Hungarian boots with gold trim and tassel. Black felt cocked hat with gold tassels.

Drummers
Troopers’ dress with black swallow nests laced yellow and six yellow lace chevrons on each sleeve. Five yellow buttonhole laces on front of coat. Copper drum stamped with rampant lion and hoops painted with alternate blue and yellow stripes or triangles.

Sappers
Grenadiers’ dress with whitened leather apron.

Infantry regiments 1809-1813

Fusiliers

• Single breasted short tailed coat in dark green cloth closed by a row of 9 buttons. Black collar piped yellow. Black shoulder straps piped yellow. Front of coat piped in yellow. Black rounded cuffs piped yellow. Black turnbacks piped yellow and vertical pockets simulated by a yellow piping. Brass buttons.
• Green vest piped yellow. Green cloth overalls with yellow Hungarian knots side bands over black or white gaiters.
• Shako as before.
• Equipment as before.

Grenadiers
Fusiliers’ dress with scarlet fringed epaulets and turnbacks bearing scarlet grenade patch. Black fur colback with scarlet cloth bag. Scarlet plume, cords and flounders. Pouch bearing a brass grenade badge and infantry sabre with scarlet strap.

Voltigeurs
Fusiliers’ dress with epaulets with yellow crescent and green fringes, turnbacks bearing yellow horn patch. Shako bearing a brass horn badge. Green plume with yellow top, yellow cords and flounders. Pouch bearing a brass horn badge and infantry sabre with green strap.

NCOs
As before.

Officers
Troopers dress with long tails and all yellow or brass ornaments becoming gold or gilded. Gold rank epaulets on shoulder and gilded gorget bearing a silver rampant lion. Sword or sabre with yellow belt worn over right shoulder and bearing a gold plate stamped with Nassau lion.

Drummers
As before.

Sappers
Grenadiers’ dress with whitened leather apron. Scarlet armband on left arm bearing a white crossed axes cloth patch. Yellow sleeved gloves.