Each Battalion kept a War Diary whilst on active service, beginning when they were deployed overseas. For the 9th King's, the 1st line (1/9th) battalion began theirs in March, 1915 whilst the 2nd line (2/9th) battalion began theirs in February, 1917. However, in January, 1918 the battalions were merged and reverted to their original '9th' designation. From this point on there was a single War Diary for the 9th King's.

March-June, 1915
July-September, 1915
October-December, 1915
January-March, 1916
April-June, 1916
July-September, 1916
October-December, 1916
January-March, 1917
April-June, 1917
July-September, 1917
October-December, 1917
January, 1918

February-March, 1917
April-June, 1917
July-September, 1917
October-December, 1917
January, 1918

February-March, 1918
April-June, 1918
July-September, 1918
October-December, 1918