21 March - 4 July 1918
This period incorporates the German attack known as Operation Michael or Kaiserschlacht
and subsequent fighting on the Somme

Scene is set: David Lloyd George commits to extend the British line

Phase: the Battle of St Quentin, 21 - 23 March 1918

Third Army (Byng)
IV Corps (Harper)
6th Division
19th (Western) Division
25th Division
41st Division
51st (Highland) Division.
V Corps (Fanshawe)
2nd Division
17th (Northern) Division
47th (2nd London) Division
63rd (Royal Naval) Division.
VI Corps (Haldane)
Guards Division
3rd Division
31st Division
34th Division
40th Division
59th (2nd North Midland) Division.

Fifth Army (Gough)
III Corps (Butler)
2nd Cavalry Division
3rd Cavalry Division
14th (Light) Division
18th (Eastern) Division
58th (2/1st London) Division.
VII Corps (Congreve)
9th (Scottish) Division
16th (Irish) Division
21st Division
39th Division.
XVIII Corps (Maxse)
20th (Light) Division
30th Division
36th (Ulster) Division
61st (2nd South Midland) Division.
XIX Corps (Watts)
1st Cavalry Division
8th Division
24th Division
50th (Northumbrian) Division
66th (2nd East Lancashire) Division.

Subsequent: the actions at the Somme crossings, 24 - 25 March 1918

Fifth Army (Gough)
VII Corps (Congreve)
39th Division.
XVIII Corps (Maxse)
3rd Cavalry Division
20th (Light) Division
30th Division
36th (Ulster) Division
61st (2nd South Midland) Division.
XIX Corps (Watts)
8th Division
24th Division
50th (Northumbrian) Division
66th (2nd East Lancashire) Division.

Phase: the First Battle of Bapaume, 24 - 25 March 1918

Third Army (Byng)
IV Corps (Harper)
19th (Western) Division
25th Division
41st Division
51st (Highland) Division
62nd (2nd West Riding) Division.
V Corps (Fanshawe)
2nd Division
12th (Eastern) Division, less 37th Brigade
17th (Northern) Division
47th (2nd London) Division
63rd (Royal Naval) Division.
VI Corps (Haldane)
Guards Division
3rd Division
31st Division
40th Division
42nd (East Lancashire) Division
59th (2nd North Midland) Division.
XVII Corps (Fergusson)
15th (Scottish) Division.

Fifth Army (Gough)
VII Corps (Congreve)
1st Cavalry Division
9th (Scottish) Division
21st Division
35th Division
37th Brigade of 12th (Eastern) Division.

Phase: the Battle of Rosieres, 26 - 27 March 1918

Fifth Army (Gough)
XVIII Corps (Maxse)
20th (Light) Division
30th Division
36th (Ulster) Division
61st (2nd South Midland) Division.
XIX Corps (Watts)
8th Division
16th (Irish) Division
24th Division
39th Division
50th (Northumbrian) Division
66th (2nd East Lancashire) Division
Carey's Force.

Phase: the First Battle of Arras, 28 March 1918

First Army (Horne)
XIII Corps (de Lisle)
56th (1st London) Division.

Third Army (Byng)
IV Corps (Harper)
41st Division
42nd (East Lancashire) Division
62nd (2nd West Riding) Division
New Zealand Division
4th Brigade of 4th Australian Division.
V Corps (Fanshawe)
2nd Division
12th (Eastern) Division.
VI Corps (Haldane)
Guards Division
3rd Division
31st Division
2nd Canadian Division
97th Brigade of 32nd Division.
XVII Corps (Fergusson)
4th Division
15th (Scottish) Division.

Phase: the Battle of the Avre, 4 April 1918

Fourth Army (Rawlinson)
Lieut-General Sir Hubert Gough was relieved of command of Fifth Army between 5-6pm on 27 March 1918. He was replaced by Sir Henry Rawlinson, hurriedly recalled from his position as British Permanent Military Representative to the Supreme War Council. Sir Henry brought in his own staff and the command became Fourth Army.
XIX Corps (Watts)
3rd Cavalry Division
14th (Light) Division
18th (Eastern) Division
24th Division
58th (2/1st London) Division
5th Brigade of 2nd Australian Division
9th Brigade of 3rd Australian Division
8th and 15th Brigades of 5th Australian Division.

Phase: the Battle of the Ancre, 5 April 1918

Third Army (Byng)
IV Corps (Harper)
37th Division
42nd (East Lancashire) Division
New Zealand Division
4th Brigade of 4th Australian Division.
V Corps (Fanshawe)
12th (Eastern) Division
47th (2nd London) Division
63rd (Royal Naval) Division.
VI Corps (Haldane)
32nd Division.
XVII Corps (Fergusson)
12th and 13th Brigades of 4th Australian Division.

Subsequent: the actions of Villers-Bretonneux, 24 - 25 April 1918

Fourth Army (Rawlinson)
III Corps (Butler)
8th Division
18th (Eastern) Division
58th (2/1st London) Division
Australian Corps (Monash)
4th Australian Division
5th Australian Division.

Subsequent: the capture of Hamel, 4 July 1918

Fourth Army (Rawlinson)
Australian Corps (Monash)
6th Brigade of 2nd Australian Division
11th Brigade of 3rd Australian Division
4th Brigade of 4th Australian Division
Two companies of 131st and 132nd Infantry Regiments of 33rd American Division were under command of 4th Australian Division and took part in this engagement.