The 12th Indian Division was formed in March 1915 from units of the British Indian Army. It formed part of the Tigris Corps, for service during the Mesopotamia Campaign of World War I. The Division arrived in Mesopotamia in April 1915 and remained there until it was broken up in March 1916. The Division's brigades remained in Mesopotamia as independent formations until forming part of the 15th Indian Division in May 1916. During its short existence it fought in a number of actions including the Battle of Shaiba between April 12–14, 1915, the Battle of Khafajiya between May 14–16, 1915, the Battle of Nasiriya between July 5, 13-14, 24 1915, where 400 British and Indian soldiers were killed in the battle and up to 2,000 Turkish Soldiers. The Occupation of Nasiriya and the affair at Butanuja, January 14, 1916.

Order of battle

The division included the following units; not all of them served at the same time:

12th Indian Brigade

30th Indian Brigade

33rd Indian Brigade

The brigade was broken up in December 1915.

34th Indian Brigade

Replaced 33rd Brigade when it was broken up.

Divisional Cavalry

Divisional Artillery

Divisional Engineers