The following units of the German First Army and British Expeditionary Force fought in the Battle of Mons in World War I.
German First Army
First Army, commanded by Generaloberst Alexander von Kluck
II Army Corps 30th Aviation Battalion 15th Foot Artillery Regiment (heavy)
3rd Infantry Division
3rd Artillery Brigade
3rd Horse Grenadiers
5th Infantry Brigade 2nd Grenadier Regiment 9th Grenadier Regiment
6th Infantry Brigade 34th Fusilier Regiment 42nd Infantry Regiment
4th Infantry Division
4th Artillery Brigade
12th Dragoons
7th Infantry Brigade 14th Infantry Regiment 149th Infantry Regiment
8th Infantry Brigade 49th Infantry Regiment 140th Infantry Regiment
III Army Corps 7th Aviation Battalion 2nd Guard Foot Artillery (heavy) 3rd Hussars
5th Infantry Division
5th Artillery Brigade
9th Infantry Brigade 8th Leib Grenadier Regiment 48th Infantry Regiment
10th Infantry Brigade 12th Grenadier Regiment 52nd Infantry Regiment
6th Infantry Division
6th Artillery Brigade
11th Infantry Brigade 20th Infantry Regiment 35th Fusilier Regiment
12th Infantry Brigade 24th Infantry Regiment 64th Infantry Regiment 3rd Jaeger Battalion
IV Army Corps 9th Aviation Battalion 4th Foot Artillery Regiment (heavy) 10th Hussars
7th Infantry Division
7th Artillery Brigade
13th Infantry Brigade 26th Infantry Regiment 66th Infantry Regiment
14th Infantry Brigade 27th Infantry Regiment 165th Infantry Regiment
8th Infantry Division
8th Artillery Brigade
15th Infantry Brigade 36th Fusilier Regiment 93rd Infantry Regiment
16th Infantry Brigade 72nd Infantry Regiment 153rd Infantry Regiment 4th Jaeger Battalion
IX Army Corps 9th Aviation Battalion 20th Foot Artillery Regiment (heavy) 16th Dragoons
17th Infantry Division
17th Artillery Brigade
33rd Infantry Brigade 75th Infantry Regiment 76th Infantry Regiment
34th Infantry Brigade 89th Grenadier Regiment 90th Fusilier Regiment 9th Jaeger Battalion
18th Infantry Division
18th Artillery Brigade
35th Infantry Brigade 84th Infantry Regiment 86th Fusilier Regiment
36th Infantry Brigade 31st Infantry Regiment 85th Infantry Regiment
III Reserve Corps
5th Reserve Division
2nd Reserve Dragoon Regiment (3 squadrons) 6th Reserve Field Artillery Regiment (6 batteries)
9th Reserve Infantry Brigade 8th Reserve Infantry Regiment 48th Reserve Infantry Regiment
10th Reserve Infantry Brigade 12th Reserve Infantry Regiment 52nd Reserve Infantry Regiment
6th Reserve Division
3rd Reserve Uhlan Regiment (3 squadrons) 6th Reserve Field Artillery Regiment (6 batteries)
11th Reserve Infantry Brigade 20th Reserve Infantry Regiment 24th Reserve Infantry Regiment
12th Reserve Infantry Brigade 26th Reserve Infantry Regiment 35th Reserve Infantry Regiment
IV Reserve Corps
7th Reserve Division
1st Reserve Schwere Reiter Regiment (3 squadrons) 7th Field Artillery Regiment (6 batteries)
13th Reserve Brigade 27th Reserve Infantry Regiment 36th Reserve Infantry Regiment
14th Reserve Brigade 66th Reserve Infantry Regiment 72nd Reserve Infantry Regiment 4th Reserve Jaeger Battalion
22nd Reserve Division
1st Reserve Jäger zu Pferde Regiment (3 squadrons) 22nd Reserve Field Artillery Regiment (6 batteries)
43rd Reserve Infantry Brigade 71st Reserve Infantry Regiment 94th Reserve Infantry Regiment 11th Reserve Jaeger Battalion
44th Reserve Infantry Brigade 32nd Reserve Infantry Regiment 82nd Reserve Infantry Regiment
10th Mixed Landwehr Brigade 12th Landwehr Infantry Regiment 52nd Landwehr Infantry Regiment
11th Mixed Landwehr Brigade 20th Landwehr Infantry Regiment 35th Landwehr Infantry Regiment
27th Landwehr Brigade 53rd Landwehr Infantry Regiment 55th Landwehr Infantry Regiment
Composite Landwehr Cavalry Unit (3 squadrons) Composite Lansturm Artillery Unit (2 batteries)
Army Troops 12th Aviation Battalion
British Expeditionary Force
British Expeditionary Force, commanded by Field Marshal Sir John French
Army Troops A and C Squadrons North Irish Horse B Squadron South Irish Horse 1st Bn Queens Own Cameron Highlanders
Line of communications defence troops 1st Devonshire 19th Infantry Brigade (formed 22 August 1914) 2nd Bn Royal Welsh Fusiliers 1st Bn Cameronians (Scottish Rifles) 1st Bn Duke of Cambridge’s Own 2nd Argyll and Sutherland Highlanders
I Corps I Corps, commanded by Lieutenant-General Douglas Haig
1st Division (Lomax)
1st Guards Brigade 1st Coldstream Guards 1st Scots Guards 1st Black Watch 2nd Royal Munster Fusiliers
2nd Infantry Brigade 2nd Royal Sussex Regiment 1st Loyal North Lancashire Regiment 1st Northamptonshire Regiment 2nd Kings Royal Rifle Corps
3rd Infantry Brigade 1st Royal West Surrey Regiment 1st South Wales Borderers 1st Gloucestershire Regiment 2nd Welsh
XXV Brigade, Royal Field Artillery 113th Battery 114th Battery 115th Battery
XXVI Brigade, Royal Field Artillery 116th Battery 117th Battery 118th Battery
XXXIX Brigade, Royal Field Artillery 46th Battery 51st Battery 54th Battery
XLIII (Howitzer) Brigade, Royal Field Artillery 30th (H) Battery 40th (H) Battery 57th (H) Battery
26th Heavy Battery Royal Garrison Artillery
2nd Division (Monro)
4th Guards Brigade 2nd Grenadier Guards 2nd Coldstream Guards 3rd Coldstream Guards 1st Irish Guards
5th Infantry Brigade 2nd Worcestershire 2nd Oxfordshire and Buckinghamshire Light Infantry 2nd Highland Light Infantry 2nd Connaught Rangers
6th Infantry Brigade 1st Liverpool Regiment 2nd South Staffordshire 1st Royal Berkshire 1st Kings Royal Rifle Corps
XXXIV Brigade, Royal Field Artillery 22nd Battery 50th Battery 70th Battery
XXXVI Brigade, Royal Field Artillery 15th Battery 48th Battery 71st Battery
XLI Brigade, Royal Field Artillery 9th Battery 16th Battery 17th Battery
XLIV (Howitzer) Brigade, Royal Field Artillery 47th (H) Battery 56th (H) Battery 60th (H) Battery
35th Heavy Battery Royal Garrison Artillery
RAMC
5th Field Ambulance
II Corps II Corps, commanded by General Horace Smith-Dorrien
3rd Division (Hamilton)
7th Infantry Brigade 3rd Bn Worcestershire Regiment 2nd Bn South Lancashire Regiment 1st Bn Duke of Edinburgh's (Wiltshire Regiment) 2nd Bn Royal Irish Rifles
8th Infantry Brigade 2nd Royal Scots 2nd Royal Irish Regiment 4th Middlesex Regiment 1st Gordon Highlanders
9th Infantry Brigade 1st Northumberland Fusiliers 4th Royal Fusiliers 1st Lincolnshire 1st Royal Scots Fusiliers
XXIII Brigade, Royal Field Artillery 107th Battery 108th Battery 109th Battery
XL Brigade, Royal Field Artillery 6th Battery 23rd Battery 49th Battery
XLII Brigade, Royal Field Artillery 29th Battery 41st Battery 45th Battery
XXX (Howitzer) Brigade, Royal Field Artillery 128th (H) Battery 129th (H) Battery 130th (H) Battery
48th Heavy Battery Royal Garrison Artillery
5th Division (Fergusson)
13th Infantry Brigade 2nd Bn Kings Own Scottish Borderers 2nd Bn Duke of Wellington’s 1st Bn Royal West Kent 2nd Bn Yorkshire Light Infantry
14th Infantry Brigade 2nd Bn Suffolk Regiment 1st Bn East Surrey Regiment 1st Bn Duke of Cornwall's Light Infantry 2nd Bn Manchester Regiment
15th Infantry Brigade 1st Bn Norfolk Regiment 1st Bn Bedfordshire Regiment 1st Bn Cheshire Regiment 1st Bn Dorsetshire Regiment
XV Brigade, Royal Field Artillery 11th Battery 52nd Battery 80th Battery
XXVII Brigade, Royal Field Artillery 119th Battery 120th Battery 121st Battery
XXVIII Brigade, Royal Field Artillery 122nd Battery 123rd Battery 124th Battery
VIII (Howitzer) Brigade, Royal Field Artillery 37th (H) Battery 61st (H) Battery 65th (H) Battery
108th Heavy Battery Royal Garrison Artillery
Cavalry Division Cavalry Division, commanded by Major-General Edmund Allenby
1st Cavalry Brigade 2nd Dragoon Guards 5th Dragoon Guards 11th Hussars
2nd Cavalry Brigade 4th Dragoon Guards 9th Lancers 18th Hussars
3rd Cavalry Brigade 4th (Queen's Own) Hussars 5th (Royal Irish) Lancers 16th (The Queen's) Lancers
4th Cavalry Brigade 6th Dragoon Guards (Carabineers) 3rd (The King's Own) Hussars Household Cavalry Composite Regiment
5th Cavalry Brigade 2nd Dragoons (Royal Scots Greys) 12th (The Prince of Wales's) Royal Regiment of Lancers 20th Hussars
Artillery III Brigade, Royal Horse Artillery D Battery, RHA E Battery, RHA VII Brigade, Royal Horse Artillery I Battery, RHA L Battery, RHA
Royal Flying Corps in the Field Royal Flying Corps, commanded by Brigadier-General David Henderson
2nd Aeroplane Squadron (Charles Burke) 3rd Aeroplane Squadron (John Salmond) 4th Aeroplane Squadron (Raleigh) 5th Aeroplane Squadron (John Frederick Andrews Higgins) 1st Aircraft Park (Carden)
Sources
Bell, Ron. “The Old Contemptibles.” Strategy & Tactics, Number 228 (May/June 2005). Terraine, John. Mons, The Retreat to Victory. Wordsworth. pp. 200–202